We have an issue with getting new certificates for our servers. It seems that this happened before and there is another thread about it.
As you can see below:
"detail": "DNS problem: query timed out looking up A for server1.test20.simplyspamfree.com", "status": 400
# letsencrypt -v --debug --staging certonly -a standalone -t --agree-tos --email email@example.com -d server1.test20.simplyspamfree.com --csr csr.der --fullchain-path fullchain.pem --keep
Please do note that this is on staging.
Also, as you can see these queries are fine from other DNS servers: