Once on one of the sites I noticed in WordPress the menu “Tools” – “Site Health” the following errors:
Rest API issued an error
…
Request to REST API failed due to error.
Error: cURL error 60: SSL certificate problem: unable to get local issuer certificate
Your site could not perform a loopback request.
…
Error: cURL error 60: SSL certificate problem: unable to get local issuer certificate
Jetpack also wrote that there is a problem with the connection to its server.
The reason was not specified by SSLCertificateChainFile in the Apache2 configuration, only the following were specified:
SSLCertificateFile /etc/letsencrypt/live/ixnfo.com/cert.pem
SSLCertificateKeyFile /etc/letsencrypt/live/ixnfo.com/privkey.pem
Therefore, I added:
SSLCertificateChainFile /etc/letsencrypt/live/ixnfo.com/chain.pem
And restarted Apache2:
sudo service apache2 restart
After this error disappeared.