That's about as clear as mud, OP. I've built more ARs than I can remember, but even a fanatic like me doesn't know about all the different brands and parts out there, so I'm having a difficult time figuring out what you're saying.
Am I understanding correctly that after putting a new handguard on your rifle it's now refusing to lock back, regardless of buffer and spring weight?
When you changed the handguard, did you also change the gas block?
ETA: One way to check gas block alignment, now that you've put some rounds through it, is pull the gas block and look at the ring of carbon around the gas port. That will tell you right away if it's misaligned. In general, though, gas blocks are cut so generous that it would have to be WAY off, like very obviously so, to restrict enough gas to cause problems.