Intermittent CURL 60 error

I’ve got some code sending a curl request via https, and using CURLOPT_CAINFO to specify the local .pem file.

What I’m finding is that I SOMETIMES get a curl 60 error (CURLE_PEER_FAILED_VERIFICATION). Maybe it’ll happen on more days than others.

What could cause this to be intermittent? I would have thought the SSL info would either be correct or not.

Use this certificate root certificate bundle
# CA certificates extracted from Mozilla

curl.cainfo = "path_to_cert\cacert.pem"

However sometimes it doesnt work because of versions etc…
See here for more : https://freefilesync.org/forum/viewtopic.php?t=6432

How can the cert be sometimes OK and sometimes not?