Not sure this will help, but hear me out. I had two kegs freeze the last gallon or so, in the serving fridge, in my kegs a few months ago, really weird. Alls they did was foam, and I knew they weren't empty based on their weight. Only other thing would be a clogged poppit, which has happened to me as well, just don't assume that only a dry hopped beer can clog a poppit, with all the debri, any beer can if not racked properly.
I recommend a cold crash and be careful when you rack to a keg. I haven't had a problem like this in a couple years. Oh yeah, and as for the frozen kegs, the fridge was freezing the kegs in the rear of the fridge, I re purposed a carboy insulator to divert the cold air directly hitting my kegs in the serving fridge, that's what was causing it.