I realized my AB sometimes tanked in my character sheet. Usually it's at 9/4 unbuffed, for some reason, it would drop to 6/1. I tested it, and it's not just the character sheet that bugs out. An actual drop to 6/1
I can fix this by swapping from my current weapon type, to something that uses a different stat. So if I'm on my sword, I switch to my bow to use dexterity, and then back. Then it fixes itself.
I notice it happening a bunch when I hop around in stealth and swap weapons a lot. So I dunno if it's tied to ranger, stances, or a bow. But the fact I fix it by swapping to a bow and then back, that might suggest it's tied to swapping between dex and str weapons, but who knows!