Thank you for this great application !
I found out a glitch which might be a bug to fix.
To reproduce the issue, use a Digital Yacht NAVLink2 hardware via Wifi connexion.
Configure qtVlm to acquire NMEA message (automated connexion for Digital Yacht hardwares) and click on launch NMEA acquisition at start.
It works pretty well as long as the wifi network is the Digital Yacht Wifi. However, if the wifi is switched to any other Wifi, qtVlm crashes. when you start to relaunch it, it immediately crashes when it tried to start the NMEA acquisition.
Workaround is pretty simple, just use your Digital Yacht Wifi (assuming you did not left it in the boat) to unclick the launch NMEA at start.
Might be good to catch this exception to prevent qtVlm to crash.
I'm using RPI4 with Debian. I reproduce the same issue on version 5.9-4 and also with the latest version.