I’m seeing a lot of JWS verification errors. It looks like we have seen this before, actually:
There are indications that this occurs when the account ID and the key is mismatched: JWS verification error · Issue #1006 · go-acme/lego · GitHub
When you migrated to your new Ubuntu instance, did you copy your Caddy data folders with it? Regardless, I’d suggest nuking it - accounts, certificates, keys, the lot, just move them to some backup folder that Caddy can’t see - and then acquiring all new certificates.