Actually could be the breathing asshole of a parasitic fly larvae. Put some petroleum jelly over it in a thick layer and see if whatever it is crawls out.
Looked like either a rupturing cyst or maybe a skin tag. I wouldn’t think it’s anything serious but I will always recommend having a vet check it. Imo it’s likely nothing but I’m also not a trained vet.
Interesting, I’ve been using jerboa since the great migration,and while it has had its moments, it’s overall been a smooth and enjoyable ride. Early on I had an issue like you’re describing with the sort types, but not in many versions. 0.0.55 is the latest play store version. Might be worth clearing data and cache and re-logging in if you are already on latest
I’m not a health expert, take this with a grain of salt. I’d be disappointed it was rusting, but also mostly shrug it off and keep using it unless it gets bad and flaky/scaley