The Client version 2.6.4 does not recognize Subject Alternative Name(s) in a Certificate. The browser doesn’t have a problem with the certificate. Observed on MacOS 10.15.5 and Kubuntu 18.04 LTS, both with client 2.6.4.
See screen from MacOS with error message and certificate details from browser connection.
The problem is not with the certificate, it is with the certificate chain. In one case, your certificate chain is incomplete. In the other, it is messed up and certificates are not ordered properly.
Use Qualys ssllabs tool to debug your SSL setup :
You select Test Your Server and put your cloud’s name in it.
Debug your setup until all chain issue are fixed.
Solved the issue by pointing to the fullchain instead of the server only.
I’m into the same issue, but with Zerossl CA.
I’ve just migrate from Letsencrypt to Zerossl, and I stumbled upon the same problem as you.
Could you explain how how did you fix it? What steps did you perform exactly?