VNC Port Forwarding

I have always been able to remote into my iMac using VNC software on iOS. About a month or two ago, VNC stopped connecting. I have not changed any of the sharing settings, and the only significant changes to the machine has been the Catalina Beta updates.

If I change the port forward rule on my router to an old Macbook pro running High Sierra, the VNC connects, but the iMac running Catalina will not connect.

Anyone else have this problem? It seems to have started after installing 10.15.4. I just installed 10.15.6, and still cannot connect.

Michael