Delete all files including the folder:
1. :\Program Files (x86)\Common Files\BattlEye
2: :\SteamLibrary\steamapps\common\Mount & Blade II Bannerlord\bin\Win64_Shipping_Client\BattlEye
3. Run Command Prompt (run as administrator)
4. sc delete BEService <---------- WRITE THAT IN THE COMMAND PROMPT, it should say that the process was successful or something along those lines
5. Preferably restart your computer. Then open Steam and Verify file integrity. Steam will say you have 6 files missing and then redownload them. That is when you will have a clean start.
Tell me if this works. Helped me when I had issues. It seems BattleEye is responsible for a lot of problems with Multiplayer
When/If you get asked if you wish to install BattleEye when you try to play Multiplayer try clicking Cancel and see if it works, it did for me. Also when installing BattleEye see that your Antivirus doesn't interfere with it. The first time I also had a BSoD. Tell me if it works. Good luck!