In Diablo+, you are getting disconnected but you can rejoin the game.
In DevilutionX, if you are unlucky then all players are getting disconnected and the game is gone.
Probably not what you would call a "crash". :-D

That can happen on TCP, but shoudn't on ZeroTier.

Diablo+ does not provide that :P

I know, that's why I didn't include it in my list: https://www.gog.com/forum/diablo/highresolution_support/post27

Good objection ... apparently we were unaware or ignorant of what ZeroTier is,so we played via TCP all the time. :-)

For TCP connection the host will be running a TCP server that repeats the network messages to all connected users. This way only the host needs to expose there port.

For ZeroTier all users connect to the same virtual network which can negotiate direct connections between players. This lets the game operate like the original as there is no distinct host for the game, but also entirely avoid the issue of port forwarding.