XCR-L Opening Itself While Firing

First, just to make sure, are the spring guide male part and lower receiver female part correct? Should the actuation nub look like this when the rifle is assembled?





Rifle is 12XXX serial number. Bought it 2nd-hand. "Competition" length upper and a 14.5" heavy barrel with pinned/welded Surefire Warcomp (dunno why the PO chose the Warcomp as the competition handguard length covers the back of the device and precludes installing a can...) Has all the ambi parts and the FAST2 stock.

I've had the rifle on a square range several times to zero different optics with no problems.

Yesterday, while on the clock at a competition, I get Bang, Bang, dead trigger. I smacked the mag and went to rack the charging handle and when I did, I almost smacked myself in the face with the operating assembly.

At some point during the cycle the rifle had opened itself and had NOT reset the trigger. It did successfully eject the empty case.

At that failure I was standing and shooting over the trunk of a prop car using the car and a large sandbag as a rest.

I put it back together and proceeded with the stage. It happened twice more during that stage - once from a similar shooting position on another car and again while kneeling and shooting from a van's dashboard.

Same thing happened while shooting prone against a barricade port at the next stage.

Was using the same ammo with which I set zero - full pressure 5.56, 62 gr. brass cased from Stand 1 Armory.

Any ideas what's could be causing this?