Did you clean the chamber with CLP and a chamber brush between outings?
Steel case ammo is coated with either lacquer or poly, and this coating gets scrapped off the rounds during loading and extraction to cause a powderized fouling that no standard gun solvent will remove.   Hence the coating powderized fouling that binds to the chamber has to be scrubbed out with a chamber brush.

Short of that, maybe a gas block that was not installed correctly and came loose/is leaking (red loctite not used on the allen bolts), or the carrier key snapped a bolt/one came loose and now you have a gas leak between the carrier and key.

The fact that the bolt is not retracting on on, is screaming a leaking gas system somewhere, so check the gas block and carrier key.
To add, when you have the B/C out, double check the inside of the carrier key.  Its not the norm, but from time to time, you can get a blow primer piece that makes it way into the key to cause blockage.