We receive the same error whenever we connect to a server in WAC - even to go to the Overview. It doesn't stop us from doing anything that we can tell so far, but is just annoying. From other forums it sounds like one thing many of us have in common is that we disable Windows Defender on servers since we have another antivirus/malware tool. I haven't seen any kind of a fix though. 1804.25 did not present this issue, 1809 does - even without having added the Windows Defender Preview module.