I wanted to suggest that the process to confirm conceding should be a little bit harder. Like, type in “CONFIRM” or your username so that you can’t subconsciously click 2 buttons and lose all your work.
I personally never had a problem with this until I did my third turn-based game in my life. Without thinking, I conceded thinking I was submitting a new move. I didn’t even realize what happened until I went to check my game later that day and found that it was “completed”.
I think there should be some type of “type to confirm concession” feature so that it isn’t so easy to quit. If you add a simple typing feature that pops up to confirm you are quitting, I’m sure the number of accidental concessions would drop to almost 0.