Most of the companies where we encounter this behavior have no idea that they are still using FRS. In fact, after seeing symptoms such as this, I cautiously ask them the question, "So... do you think it's possible that you guys are still running FRS instead of DFSR?" and they always answer, "No way! We ditched FRS long ago!" But... so far I have a 100% success rate for being right; when we query Active Directory, we find that, sure enough, they are still using FRS.
You can only utilize one or the other to sync data between Domain Controllers. You have either cut your environment over to DFSR, or you are still running FRS. Don't automatically assume that just because you have Server 2016 Domain Controllers running in ...
