After running sudo apt update and upgrade (as well as postinstall) openplotter info complained about conflicting ports in AvNav.
As it turned out, the newly added avnav updater was setup by the installer with port 8080 (same as viewer)
Setting it manually to default 8085 (as documented) fixed the problem.
As no port settings had been modified before, this appears to be a bug in the install/update process
After running sudo apt update and upgrade (as well as postinstall) openplotter info complained about conflicting ports in AvNav. As it turned out, the newly added avnav updater was setup by the installer with port 8080 (same as viewer)
Setting it manually to default 8085 (as documented) fixed the problem. As no port settings had been modified before, this appears to be a bug in the install/update process