Ejection distance (spent case out 10'~15') is a better indicator of how the stroke is doing, since could be other problems on why the mag was not locking back. So here, instead of looking at angle of ejection (since could be a forward path after rearward ejection of the case hits the upper defector to redirect it back forward), look at the over all distance of the spent case instead.
On the charging handle pull, is the last inch of pull the same in tension as the middle of pull? Hence is something going on that the last inch of bolt travel has binding problems, and maybe the reason that the bolt is not coming far enough back to get behind the catch.
With upper shotgun open, shove the empty mag ( with its follower pushed all the way forward in it) all they way forward in the well as you lock it into the well, and make sure that bolt catch tab is not coming up short against the back shelf of the follower to raise it up.
Also, make sure that the bolt catch is not binding in the lower, and just has the normal spring tension pulling it back.
As for lube being used, Should only be CLP. So on that note, clean the rig with CLP to remove all the grease and other lubes (CLP has a cleaning agent in it), then once the grease fouled CLP is removed, apply a new fresh coat of CLP to the upper receiver bearing areas. Hence CLP not only has a cleaning agent in it to keep the rig from fouling chocking itself out/will not collect fouling, but has a temp range of use from -60 to +160 °F.
As for the gas adjustment (and possible other parts of the gas system as well), when some adjuster are screwed all the way out, tend to leak, so what would be the normal amount of pressure out of the barrel gas port to action, is lost in the leakage. Hence unless the rig is well over gassed that needs to be resolved (that a heaver buffer can not just solve isntead), and the gas pulse needs to be reduced, best to just run a standard gas block instead. On the same note, would check the rest of the gas system for leakages, hence block to barrel, gas tube to block, and even carrier key to top of carrier.