So, I'm going to make several suggestions.
Caution: Take the real bullets and put them in another room.
1.) Lubricate this gun. Lubricate it like it's going to have to be shipped back to Glock if this idea doesn't work.
Cycle the 5-10 times. Oil the back of the barrel, slide, the front of the barrel, under up into the gun mag well.
2.) Re-install the striker assembly, extractor, back plate, etc.
3.) Grab your snap cap, load it in a magazine and attempt to cycle it - see if it will load it. I believe (and it's been months...) that worked for me. But then, you have a snap cap loaded and not a real bullet, so you can pull the trigger (not launch a round through your house, etc.), and if this works, depress the trigger, pull down the ears and bob's your uncle she's taken apart. Look for any oddities. I could not find anything and never ran into it again (as you can observe in the attached photo... she's seen a few rounds since then).
4.) If this doesn't work let's attempt the following. Load that snap cap into the magazine, let the slide go and chamber that as far as it will. I've attached an image of the back of a snap cap looking into the mag well (the iPhone didn't focus great, but you see enough to know what you're looking at and I circled it in red, etc.). This is fully seated and round chambered for reference. You should see more of the back of a not yet chambered round. From that point, take a punch set (something small diameter, but round enough), and tap it and see if it'll seat further forward. Don't go wild with this, but I think give it several light taps and see what happens. Make sure you've oiled the top of the barrel as it lock into battery. Worst case scenario you mar up a snap cap some. (ETA: What I'm picturing is you're producing upward pressure on the base of the snap cap from the bottom of the gun to try to push the barrel up and into battery, etc.)
Attachment 99184
If this doesn't work, I might try without the striker, extractor, and back plate, etc. as well.
I would also contact Glock as well. I might try seating a magazine (with snap caps) firmly and tapping the bottom of it as well just to see what happens, but I wouldn't push on the slide anymore as I don't think that's going to resolve this, but I could be wrong. Try slide lock, insert mag with snap cap, and hitting the slide release. Again, if it chambers a snap cap you can take it apart.
Food for thought - I'll say a prayer for you man! I hope this turns around. I love my Gen 5 Glock 34's.