Ok, so I check in a couple of days ago, and someone else became mayor later that day. By game math, that should never have happened. Ties always default to the current mayor, so once you check in for the day, you are safe. There's no way for someone to have more check-ins than you if you are both checking in every day and you have checked in first. The most you can have is a tie, and the ties resolve to the current mayor. I thought maybe the bug was just a delayed notification and he'd checked in earlier than I had that day.
The next day when I check in, it says I'm two days away from becoming mayor. Another thing that should never happen. I've been checking in every day, and there are no negative check-ins.
Then the next day, the screen still says that I have 29 and that he has "31 check-ins in 30 days." Only one check-in should count towards this score per day per game rules. So either it's not counting my check-ins or it's overcounting his.
So then I realize that the only location app I currently cared about enough to put up with bugs like this was Pokemon Go. The end.