Ok, some time passed after I posted this and nothing changed, I'll try to put it more simply maybe then devs will understand when you relay this to them. If this won't work I'll post pictures of whole process. It should be easy fix.
1) Join a skirmish or captain ranked game(joining implies you are actually in game not in lobby waiting)
2) For easier troubleshooting wait for warmup to end and real match to start as otherwise new 'leaver penalty might hit you'
3) When real match starts after warmup: alt+f4/kill bannerlord process or disable your inet connection
4) Restart bannerlord
5) After restarting bannelord you get a prompt asking(everything is greyed out at same time and you cant click anything except those 2 options below):
DO YOU WANT TO REJOIN PENDING MATCH?*
RECONNECT NO
6) Select RECONNECT
7) You clicked reconnect. No after like 1-3 seconds you'll be able to freely navigate in main menu as if reconnecting didnt work. In this time you can click on 'find game' in the middle bottom of the screen. If you do that you'll crash.. What exactly happens: you can see timer starting 'looking for game' but in few seconds (2-3?) you get reconnected to your old game. When map loads, players get loaded and you briefly can see their classes at top of the screen. This is when crash happens
Hoe to fix: Make 'find game' unclickable in main menu when you try to reconnect; or just make whole main menu unnacesible which is already happening when you get reconnect/no prompt(just maybe make some timer on it so you aint stuck if reconnecting doesnt work? 10-30secs? idk)
*i dont exactly remember what prompt says but it's kinda straighforward.
PS. This isn't really critical to fix, only if you are too eager to play/find new match fast and click on 'find game' this will happen. There are more pressing matters to be fixed in multi. If fixing this random crap would take much time.. just leave it be.