Can't connect to Raspberry pi after updating to 7.11.1

Scenario:

I have a Raspberry Pi 2b running the latest os distro. It's been running 24/7 for several years. It is used as an Mqtt broker and Node Red dashboard server. I usually run apt update / upgrade from the cli via RealVNC. I also have a 3b as a standby in the event the 2b crashes. Since recently I'd been seeing notification that an updated version of RealVNC was available I did a reinstall with the new version only on the 3b. But when I try to log on to the 3b I get an error stating:

An authentication error occurred.  See the VNC Server error log for details.

I did not update the 2b and can still log on to it. 
What am I missing?