Just pushed out an update to address some issues/crashes that would occur if the server restarted during your adventure run - it was causing a desync between the client and the server, leading to either a failed battle or a straight out game crash
These should be fixed now. If you still run into game randomly erroring out, try going back to lobby then continuing the adventure from there, it should resolve most issues. I will be working on making those issues more graceful in an upcoming major update