From the slide show photos you listed,
If any are of the bolt face with the charging handle pulled back, the bolt is not retracted back far enough from the bolt catch, but we know this from the start with the void of the tube being short to start with. So on that note, one of the buffer bumpers will need to be mod'd/ buffer bumper shortened to allow the bolt face to retract far enough behind the catch to allow the mag follower to get the catch up at the back of stroke, before the bolt starts moving forward from the back of stroke isntead.
But, I going to take this one step deeper, since not a fan of the way the receiver extension is mounted in the lower receiver, and the buffer sticking way to far out of it with the upper open.
So step one, we are going to mod/set back the lower receiver extension lip so it can be threaded in one more turn, with the face of the bottom lip kissing the center post of the buffer retaining pin. Hence I want the upper end lip of the tube dam near flush with the inside edge of the lower receiver threaded ring surface isntead.
Hence forget about the bottom protruding lip for a second, and here is the relation ship I want with the top of the tube end of lip to the inside face of the thread ring on the lower receiver (read dam near flush with each other, with at most, the tube end face only lightly back from the face of the tube a few thousands of an inch, and now where near the plus I turn you have it now).
Now with this done, we need to mod/shorten one of the buffer bumpers to achieve the desired bolt face with full charging charging handle pull retraction distance so the face of the bolt is only 1/8" to 1/4" in front of the back edge of the ejection port.
Note: counted the spring coils on the spring with buffer, and since it 39 coils, it good to use as it is.
Here is where you are now if this is a full charging handle pull (got to be, since I don't see the raise bolt catch in front of the bolt face holding the bolt back isntead).
And yes, the way the bolt catch works, is by the bolt face retracting back behind the catch to raise up in front of the bolt face, and not just catching the bottom of the carrier instead.
Here is where it should be instead with the charging handle pulled all the way back, and the buffer bumper shortened to allow such. Again, front face of the bolt, to the back edge of the ejection port window being 1/8" to 1/4". hence this walls the bolt to retract back behind the bolt catch far enough, that is allow the empty mag follower to raise up in front of the bolt before it starts moving back forward again.
Bolt catch holding the bolt back via is face, so again, bolt has to retract back the catch enough at bolt of stroke, to get the mag follower enough time to get it up in front of the bolt before it come back to the bolt catch. As for why we don't want the bolt face to retract past the back of the ejection port, then spent cases as pivot off the bolt face at the back of stroke during the buffer stall, and we don't want them to tag the back inside edge of the ejection port window to deflect the spent rounds back into the action to cause a stove pipe jam,
Now lets move onto this, hence you mention a hand guard change as well,
So lets be blunt, did you remove the FSB,Gas block and even barrel nut to change out the front hand guard? If you did not touch any of these, and the only thing you did was pull back on the delta ring to slip the guards open to remove them, then install another set of slip guards back on the barrel/delta nut/front hand guard clip, then no problem. here, all I need you to do is to pull the bolt off the carrier and with the carrier and key, just dry fit them to the upper receiver to make sure that the carrier moves freely in the upper receiver, and the gas tube is indexed with the carrier key (end of gas tube will enter the carrier key when the front of the carrier is about an inch from the front off touching the back of the barrel extension.
But if the FSB, gas block/FSB was removed, then we need to go back and start addressing possible problem with the barrel receiver index timing to the upper receiver, the FSB/gas block gas passage indexing to the barrel gas port, and even barrel nut to gas block channel and even gas tube indexing to carrier key as well. I bring this up since you do not post a photo of the front end of the upper receiver so see what was changed there.
Also to bring it back to the spent case, please tell me that you are using an Ar-15 chamber brush with CLP to clean the chamber by hand during cleanings.
I bring this up, since the spent case just before the shoulders look less than stellar from a dirty chamber that was not fully cleaned each cleaning instead.