The fact that it's 16 months old - an adolescent - probably has a whole lot to do with it. Adolescent dogs are hard to deal with and no longer cute like puppies, so you see them end up being rehomed, dumped, etc. quite a bit.

Also, APBT and mixes are often prone to dog aggression and sometimes human aggression, and those things frequently don't show up until the dog is fully mature, so in the 2-3 year old range - which means there's a lot of unknown still to come.