Here's a debug log of the resolution from a production VA resolver:
Sep 13 17:50:19 info: resolving _acme-challenge.abisoft.spb.ru. TXT IN
Sep 13 17:50:19 info: priming . IN NS
Sep 13 17:50:19 info: response for . NS IN
Sep 13 17:50:19 info: reply from <.> 2001:7fe::53#53
Sep 13 17:50:19 info: query response was ANSWER
Sep 13 17:50:19 info: priming successful for . NS IN
Sep 13 17:50:19 info: response for _acme-challenge.abisoft.spb.ru. TXT IN
Sep 13 17:50:19 info: reply from <.> 198.97.190.53#53
Sep 13 17:50:19 info: query response was REFERRAL
Sep 13 17:50:19 info: resolving b.dns.ripn.net. AAAA IN
Sep 13 17:50:19 info: resolving f.dns.ripn.net. A IN
Sep 13 17:50:19 info: resolving a.dns.ripn.net. AAAA IN
Sep 13 17:50:19 info: resolving f.dns.ripn.net. AAAA IN
Sep 13 17:50:19 info: resolving b.dns.ripn.net. A IN
Sep 13 17:50:19 info: response for a.dns.ripn.net. AAAA IN
Sep 13 17:50:19 info: reply from <.> 192.36.148.17#53
Sep 13 17:50:19 info: query response was REFERRAL
Sep 13 17:50:19 info: response for b.dns.ripn.net. A IN
Sep 13 17:50:19 info: reply from <.> 2001:500:2::c#53
Sep 13 17:50:19 info: query response was REFERRAL
Sep 13 17:50:19 info: response for f.dns.ripn.net. A IN
Sep 13 17:50:19 info: reply from <.> 198.97.190.53#53
Sep 13 17:50:19 info: query response was REFERRAL
Sep 13 17:50:19 info: response for f.dns.ripn.net. AAAA IN
Sep 13 17:50:19 info: reply from <.> 2001:500:2::c#53
Sep 13 17:50:19 info: query response was REFERRAL
Sep 13 17:50:19 info: response for b.dns.ripn.net. AAAA IN
Sep 13 17:50:19 info: reply from <.> 2001:500:2::c#53
Sep 13 17:50:19 info: query response was REFERRAL
Sep 13 17:50:19 info: response for b.dns.ripn.net. A IN
Sep 13 17:50:19 info: reply from <net.> 2001:500:856e::30#53
Sep 13 17:50:19 info: query response was REFERRAL
Sep 13 17:50:19 info: response for f.dns.ripn.net. A IN
Sep 13 17:50:19 info: reply from <net.> 2001:503:a83e::2:30#53
Sep 13 17:50:19 info: query response was REFERRAL
Sep 13 17:50:19 info: response for f.dns.ripn.net. AAAA IN
Sep 13 17:50:19 info: reply from <net.> 2001:502:7094::30#53
Sep 13 17:50:19 info: query response was REFERRAL
Sep 13 17:50:19 info: response for b.dns.ripn.net. AAAA IN
Sep 13 17:50:19 info: reply from <net.> 2001:500:856e::30#53
Sep 13 17:50:19 info: query response was REFERRAL
Sep 13 17:50:19 info: response for a.dns.ripn.net. AAAA IN
Sep 13 17:50:19 info: reply from <net.> 192.43.172.30#53
Sep 13 17:50:19 info: query response was REFERRAL
Sep 13 17:50:19 info: response for _acme-challenge.abisoft.spb.ru. TXT IN
Sep 13 17:50:19 info: reply from <ru.> 193.232.128.6#53
Sep 13 17:50:19 info: query response was REFERRAL
Sep 13 17:50:19 info: resolving ns4-geo.nic.ru. AAAA IN
Sep 13 17:50:19 info: resolving ns8-geo.nic.ru. A IN
Sep 13 17:50:19 info: resolving ns3-geo.nic.ru. AAAA IN
Sep 13 17:50:19 info: resolving ns4-geo.nic.ru. A IN
Sep 13 17:50:19 info: resolving ns8-geo.nic.ru. AAAA IN
Sep 13 17:50:19 info: resolving ns3-geo.nic.ru. A IN
Sep 13 17:50:19 info: response for f.dns.ripn.net. AAAA IN
Sep 13 17:50:19 info: reply from <ripn.net.> 2001:678:17:0:193:232:128:6#53
Sep 13 17:50:19 info: query response was ANSWER
Sep 13 17:50:19 info: response for f.dns.ripn.net. A IN
Sep 13 17:50:19 info: reply from <ripn.net.> 2001:678:17:0:193:232:128:6#53
Sep 13 17:50:19 info: query response was ANSWER
Sep 13 17:50:19 info: response for b.dns.ripn.net. AAAA IN
Sep 13 17:50:19 info: reply from <ripn.net.> 194.85.252.62#53
Sep 13 17:50:19 info: query response was ANSWER
Sep 13 17:50:19 info: response for b.dns.ripn.net. A IN
Sep 13 17:50:19 info: reply from <ripn.net.> 193.232.142.17#53
Sep 13 17:50:19 info: query response was ANSWER
Sep 13 17:50:19 info: response for a.dns.ripn.net. AAAA IN
Sep 13 17:50:19 info: reply from <ripn.net.> 2001:678:15:0:193:232:142:17#53
Sep 13 17:50:19 info: query response was ANSWER
Sep 13 17:50:20 info: response for ns8-geo.nic.ru. AAAA IN
Sep 13 17:50:20 info: reply from <ru.> 2001:678:17:0:193:232:128:6#53
Sep 13 17:50:20 info: query response was REFERRAL
Sep 13 17:50:20 info: response for ns4-geo.nic.ru. A IN
Sep 13 17:50:20 info: reply from <ru.> 194.85.252.62#53
Sep 13 17:50:20 info: query response was REFERRAL
Sep 13 17:50:20 info: response for ns3-geo.nic.ru. AAAA IN
Sep 13 17:50:20 info: reply from <ru.> 193.232.128.6#53
Sep 13 17:50:20 info: query response was REFERRAL
Sep 13 17:50:20 info: response for ns8-geo.nic.ru. A IN
Sep 13 17:50:20 info: reply from <ru.> 2001:678:15:0:193:232:142:17#53
Sep 13 17:50:20 info: query response was REFERRAL
Sep 13 17:50:19 info: query response was ANSWER
Sep 13 17:50:20 info: response for ns8-geo.nic.ru. AAAA IN
Sep 13 17:50:20 info: reply from <ru.> 2001:678:17:0:193:232:128:6#53
Sep 13 17:50:20 info: query response was REFERRAL
Sep 13 17:50:20 info: response for ns4-geo.nic.ru. A IN
Sep 13 17:50:20 info: reply from <ru.> 194.85.252.62#53
Sep 13 17:50:20 info: query response was REFERRAL
Sep 13 17:50:20 info: response for ns3-geo.nic.ru. AAAA IN
Sep 13 17:50:20 info: reply from <ru.> 193.232.128.6#53
Sep 13 17:50:20 info: query response was REFERRAL
Sep 13 17:50:20 info: response for ns8-geo.nic.ru. A IN
Sep 13 17:50:20 info: reply from <ru.> 2001:678:15:0:193:232:142:17#53
Sep 13 17:50:20 info: query response was REFERRAL
Sep 13 17:50:20 info: response for ns3-geo.nic.ru. A IN
Sep 13 17:50:20 info: reply from <ru.> 2001:678:18:0:194:190:124:17#53
Sep 13 17:50:20 info: query response was REFERRAL
Sep 13 17:50:20 info: response for ns4-geo.nic.ru. AAAA IN
Sep 13 17:50:20 info: reply from <ru.> 194.190.124.17#53
Sep 13 17:50:20 info: query response was REFERRAL
Sep 13 17:50:20 info: response for ns8-geo.nic.ru. AAAA IN
Sep 13 17:50:20 info: reply from <NIC.RU.> 31.177.74.100#53
Sep 13 17:50:20 info: query response was nodata ANSWER
Sep 13 17:50:20 info: response for ns4-geo.nic.ru. A IN
Sep 13 17:50:20 info: reply from <nic.ru.> 31.177.67.100#53
Sep 13 17:50:20 info: query response was ANSWER
Sep 13 17:50:20 info: response for ns3-geo.nic.ru. AAAA IN
Sep 13 17:50:20 info: reply from <nic.ru.> 2a02:2090:e400:7000:31:177:85:186#53
Sep 13 17:50:20 info: query response was nodata ANSWER
Sep 13 17:50:20 info: response for ns8-geo.nic.ru. A IN
Sep 13 17:50:20 info: reply from <nic.ru.> 2a02:2090:ec00:9040:31:177:74:100#53
Sep 13 17:50:20 info: query response was ANSWER
Sep 13 17:50:20 info: response for ns3-geo.nic.ru. A IN
Sep 13 17:50:20 info: reply from <nic.ru.> 2a02:2090:e800:9000:31:177:67:100#53
Sep 13 17:50:20 info: query response was ANSWER
Sep 13 17:50:20 info: response for ns4-geo.nic.ru. AAAA IN
Sep 13 17:50:20 info: reply from <nic.ru.> 31.177.67.100#53
Sep 13 17:50:20 info: query response was nodata ANSWER
Sep 13 17:50:29 info: resolving _acme-challenge.abisoft.spb.ru. TXT IN
Sep 13 17:50:29 info: resolving ns4-geo.nic.ru. AAAA IN
Sep 13 17:50:29 info: resolving ns8-geo.nic.ru. AAAA IN
Sep 13 17:50:29 info: resolving ns3-geo.nic.ru. AAAA IN
Sep 13 17:50:51 info: Capsforid: timeouts, starting fallback
Sep 13 17:51:07 info: control cmd: stats_noreset
Sep 13 17:51:13 info: resolving ns4-geo.nic.ru. AAAA IN
Sep 13 17:51:13 info: resolving ns4-geo.nic.ru. A IN
Sep 13 17:51:14 info: response for ns4-geo.nic.ru. A IN
Sep 13 17:51:14 info: reply from <ru.> 2001:678:17:0:193:232:128:6#53
Sep 13 17:51:14 info: query response was REFERRAL
Sep 13 17:51:14 info: response for ns4-geo.nic.ru. AAAA IN
Sep 13 17:51:14 info: reply from <ru.> 193.232.142.17#53
Sep 13 17:51:14 info: query response was REFERRAL
Sep 13 17:51:14 info: response for ns4-geo.nic.ru. A IN
Sep 13 17:51:14 info: reply from <NIC.RU.> 2a02:2090:e800:9000:31:177:67:100#53
Sep 13 17:51:14 info: query response was ANSWER
Sep 13 17:51:14 info: response for ns4-geo.nic.ru. AAAA IN
Sep 13 17:51:14 info: reply from <NIC.RU.> 31.177.85.186#53
Sep 13 17:51:14 info: query response was nodata ANSWER
Sep 13 17:51:14 info: resolving ns8-geo.nic.ru. AAAA IN
Sep 13 17:51:14 info: resolving ns8-geo.nic.ru. A IN
Sep 13 17:51:14 info: response for ns8-geo.nic.ru. A IN
Sep 13 17:51:14 info: reply from <ru.> 193.232.156.17#53
Sep 13 17:51:14 info: query response was REFERRAL
Sep 13 17:51:14 info: response for ns8-geo.nic.ru. A IN
Sep 13 17:51:14 info: reply from <NIC.RU.> 31.177.85.186#53
Sep 13 17:51:14 info: query response was ANSWER
Sep 13 17:51:15 info: response for ns8-geo.nic.ru. AAAA IN
Sep 13 17:51:15 info: reply from <ru.> 2001:678:18:0:194:190:124:17#53
Sep 13 17:51:15 info: query response was REFERRAL
Sep 13 17:51:15 info: response for ns8-geo.nic.ru. AAAA IN
Sep 13 17:51:15 info: reply from <nic.ru.> 31.177.74.100#53
Sep 13 17:51:15 info: query response was nodata ANSWER
Sep 13 17:51:15 info: resolving ns3-geo.nic.ru. AAAA IN
Sep 13 17:51:15 info: resolving ns3-geo.nic.ru. A IN
Sep 13 17:51:15 info: response for ns3-geo.nic.ru. AAAA IN
Sep 13 17:51:15 info: reply from <ru.> 194.85.252.62#53
Sep 13 17:51:15 info: query response was REFERRAL
Sep 13 17:51:15 info: response for ns3-geo.nic.ru. AAAA IN
Sep 13 17:51:15 info: reply from <nic.ru.> 31.177.67.100#53
Sep 13 17:51:15 info: query response was nodata ANSWER
Sep 13 17:51:15 info: response for ns3-geo.nic.ru. A IN
Sep 13 17:51:15 info: reply from <ru.> 194.190.124.17#53
Sep 13 17:51:15 info: query response was REFERRAL
Sep 13 17:51:15 info: response for ns3-geo.nic.ru. A IN
Sep 13 17:51:15 info: reply from <nic.ru.> 31.177.85.186#53
Sep 13 17:51:15 info: query response was ANSWER
Sep 13 17:51:20 info: resolving _acme-challenge.abisoft.spb.ru. TXT IN
Sep 13 17:51:36 info: resolving _acme-challenge.abisoft.spb.ru. TXT IN
Sep 13 17:51:36 info: priming . IN NS
Sep 13 17:51:36 info: response for . NS IN
Sep 13 17:51:36 info: reply from <.> 2001:500:2f::f#53
Sep 13 17:51:36 info: query response was ANSWER
Sep 13 17:51:36 info: priming successful for . NS IN
Sep 13 17:51:36 info: response for _acme-challenge.abisoft.spb.ru. TXT IN
Sep 13 17:51:36 info: reply from <.> 192.33.4.12#53
Sep 13 17:51:36 info: Capsforid: reply is equal. go to next fallback
Sep 13 17:51:36 info: response for _acme-challenge.abisoft.spb.ru. TXT IN
Sep 13 17:51:36 info: reply from <.> 2001:7fe::53#53
Sep 13 17:51:36 info: Capsforid fallback: getting different replies, failed
Sep 13 17:51:37 info: control cmd: stats_noreset
Sep 13 17:52:07 info: control cmd: stats_noreset
So this appears to be a capsforid problem coming out of the annals of Let's Encrypt validation history.