Latest update:
I took a bit more careful look at the rifle to try to determine the random bolt lock backs and realized that there was minimal spring tension on the bolt release. Knocked the pin out and sure enough the detent was stuck too deep in the spring hole. I have been down this road with at least one AR15 and it appeared to be the same problem- The opening around the detent got peened over and was preventing it from extending properly.
I took out the awl on my multi-tool, poked the detent in with the point and reamed out the offending material with the blade part. I think last time I did this I used a tiny file and a small drill bit (used by hand) would also accomplish the same thing. It's really just a thin bit of material that needs to be removed. Since it's not uncommon on AR15's I'm sure someone has a Youtube video about it.
Anyway now #2 is running good.