It looks to me the OCSP server of Identrust is down.
Usually few clients do OCSP checks of the intermediate cert, thus this probably doesn’t show up very often. I noticed because I have some monitoring set up using gnutls-cli with ocsp checks to verify if certificates are okay.
You can check e.g. with:
gnutls-cli --ocsp letsencrypt.org:443
This is what I get:
Connecting to OCSP server: isrg.trustid.ocsp.identrust.com…
Connecting to ‘2a02:26f0:3100::1735:2a09:80’…
importing response: ASN1 parser: Error in TAG.
(There’s a curious behavior of gnutls that it does not check the ocsp of the intermediate if the server runs ocsp stapling, so this only reproduces on servers without stapling.)