I just picked up a Daniel Defense M4 v11. Upon arrival I installed a Geissele trigger and a Phase 5 extended bolt release (EBRv2) and lubed everything up with some frog lube. Took it to the range and ran 5 new magpul PMAGS filled with 5.56 PMC X-TAC 55gr. thru without a hitch. Went home, ran a patch thru the barrel, re-lubed and put the gun away. The next weekend I take the gun and my father to the range and now it doesn't lock back on an empty magazine after the last shot. It DOES lock back on  an empty mag when you pull the CH without fail. I've changed nothing from the first time I took it out, and I'm lost. I tried some hexmags, and a different EBR from another rifle with the same issue. ANY help would be greatly appreciated.

I have zero experience with frog lube but have heard many tales about what can happen if not applied correctly. I'll take a shot in the dark and say you have a bunch of excess frog lube gumming up the spring under your bolt catch.
Improper frog lube application testimony
If you take the rear takedown pin out and split your rifle open, try working your bolt catch with your finger and see if it feels gummed up or if it feels like it is moving freely.
Keep in mind I have no experience using frog lube personally and I'm not saying that it sucks or it is awesome stuff. I'm just passing along what I have heard.

I went pretty light, but I did leave a little more than a film. I broke it down and everything seems to be moving freely. I put these Phase 5 EBR's on 2 other AR's I just finished and they run perfectly. It's the just the DDM4 that's giving me an issue. It worked fine for 5 mags and the next range trip, nothing. Also, with an empty magazine inserted the bolt locks back when you charge it without fail. It's almost like it's short stroking, but it feeds and ejects perfectly..... Out of desperation I put the factory bolt release back on. I'll see what that does tomorrow.

While you were swapping the releases out, did you notice anything unusual about the spring or little compartment it fits in? Was it sticky or?

Seemed normal enough to me, but I did swap out the spring for a new one. The old one seems fine, but I had it apart....

Every time that's happen to one of my AR's it was a loose gas key. One wasn't loose enough to wiggle about but it wouldn't lock back. Retorqing it fixed the leak and it worked correctly. This was way back when Bushmaster hadn't figured out how to tighten gas keys correctly...