The ceiling in the bathroom has this funky looking bubble

[Mohammad Ashori]

The bathroom doesn't have a vent so it gets moisture building up. It has a window but this is Portland, it's not really that much dryer opening the windows.

So I just bought this condo and 2 years ago and I noticed this little bubble that's dry and brittle. Dunno how long it's been there. Had tenants in it before and they didn't see any water dripping or anything like that. 

Any suggestions on next step? I'm a DIY-er