And yes, as you said BUTT still connects - but it could be possible that the firewall settings has been changed by accident or by Windows without your knowledge for “safety” reasons especially for the mAirList application…
It may even be possible that the windows defender overruled the settings for mAirList in the background - we highly suggest to set an exception rule for the mairlist.exe and the mAirList folder too.
The user in the linked thread finally solved the error 40 problems by following this advice (save your config as a backup!) but I would take a look at the firewall and defender settings first…