Some users who are on OpenSSL 1.0 reported getting an SSL error, saying that our certificate expired. The certificates are not expired, but an old root certificate (DST Root CA X3) did expire, and that's causing issues with OpenSSL 1.0. Read more here: https://letsencrypt.org/docs/dst-root-ca-x3-expiration-september-2021/
Upgrading OpenSSL to 1.1 or later fixes the issue.
We will, from our side, see if there are things we can do to work around this issue.