SSL error with mbsync
This is a certificate issue. In my .mbsyncrc, I included as CertificateFile the entire certificate chain (Gmail -> Google, Google -> GeoTrust, GeoTrust -> Equifax). This started intermittently throwing the error you're describing around the time I fixed the curl SSL issue.

To fix it, use only the Gmail certificate in your .mbsyncrc. If you're unsure which of the certificates is the Gmail one, run: 

openssl s_client -connect imap.gmail.com:993 -showcerts 2&gt;&amp;1 &lt; /dev/null | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' | head -n 27 &gt; gmail.crt


and use the resulting gmail.crt file.