We had a crash based on someone selecting buddy mode spawn. This caused a crash due to my not completely testing Buddy Mode with the new Character Mode option. This has been fixed in 4.2.29, thanks Trophium and Spzi for running some tests that exposed the root cause.

Root cause: I require that players on the same team be of the same spawn type - Character or Brave New Player modes. Character is how you play normal Factorio, offers crafting and inventory in your character. Brave New Player is the mode where you can only carry some items, can't craft anything and do not have a character. A team must be of the same type - since some settings impact the whole force/team and that would impact the characters ability to hold items in it's inventory and craft/mine. If your team is all of the same type - these conflicts do not occur.

The checkbox button behind the choice of character mode enforces this mode choice, if someone has already spawned on the MainForce then the checkbox is forced into the position of that first persons selection. If you want to make your own choice of character/BNO Player then make your own team or join a team that has the option you desire. Use the menus to see each players choices.