So far the issues we've had
- Applying certificate to Portal breaks access to portaladmin, meaning you cannot access the portal admin tool after you apply the certificate. There is a known workaround of resetting a config file to allow access but applying the cert will break it
- From what I have read this may be only an issue with wildcard certs. I would certainly expect esri's https to work with wildcard certs as this is a very common approach in companies that use https.
- Sync with a archive database (esri's recommended approach) is completely broken in 10.5.1.
Fortunately, we setup a dev environment prior to moving production to 10.5.1, it doesn't seem this version is very stable or was tested prior to release