I was installing a Magpul Backpacker stock this evening, and lo and behold the locking block on the barrel was actually quite loose after years of use. Because of how the factory stock fits, I had no idea as the main screw holds everything tightly. It took all of three minutes to disassemble the block, clean it up, and reassemble to ensure it's tight.

I ad exactly the same issue, the difference in my case is that my POI actually starts to shift randomly, I blamed the scope first till someone reminded me to check the screws.

Was there any threadlocker from the factory?

I'd put some blue loctite on it to be sure.

Looks like there could've been, but it wasn't much. I did put some on them this time.

Just to clarify, this post isn't referring to the bolts in the receiver, but to the spring loaded block attached to the barrel itself.

Are there known torque values?

Spent a few minutes looking and unlike the bolts in the receiver block, I couldn't find it. The YT guide I watched just suggests snug enough to keep them from lossening.

20 in-lb I think.