Damn, I noticed this issue some days ago and thought it's just an exception..
I always take portrait photos of people, as it looks incredibly good, especially on this phone. I don't mind waiting (Even though it's very awkward when you say "this phone takes good pictures, but we'll wait a minute for each"), but after like three photos, the camera app won't allow me to take another, and I'll have to wait until at least one is processed.
Waiting is one thing, but not being able to take another shot before it's processed is very very annoying.
I also noticed that Google photos generally has very slow processing, it feels way slower than my old P6P and even the P5. Maybe the new Tensor chip isn't used fully, even if that's the whole reason for Tensor to exist.