Hmmm

Yep, I need to take some time off from upper body training.

Many times doing the opposite of what you want to achieve, is what needs to be done. Want to get better at doing high repetition push ups and pull ups, and it is just not happening- maybe its time to focus on legs and perform max attempt weighted push ups and pull ups.

I call it the principle of duality. Everything in the body has a duality to it. You have antagonistic muscles, you have slow twitch and fast twitch fibers, you have catabolic and anabolic cycles, you have a sympathetic and parasympathetic nervous system, we could do this for days. To improve one, you sometimes have to look at the other.

Why is your body failing to anabolize? Maybe it needs a little time off to catabolize. Why can't you increase strength? Maybe because your endurance and recovery sucks and your nervous systems is fried from all the max effort squats. You get the drift. Its the basic principle of physiology. If you want a nicer sounding term, go for negative feedback loop. Maybe now it will make more sense.
Cheers.