That was my first thought also.
I replaced the CPA block and I keep that one in the photo for a spare in case for a firing pin brakes for a quick change during a match. The flame cuts stopped when I quit using the under primer and under powder wads. I still use the same brass.
The .50 Shiloh I have used in the past more than any of my Rifles and I kept track with the amount of primer bricks I used by numbering them, but I lost count after 21 bricks during the primer shortage during Obama's time I would say it has most likely have over 25K rounds shot through it and I still use the same brass and the flame cuts stopped when I quit fooling around with the wads. So I feel loose primers were not the cause.
One thing that might have some issues is the heavy compressed load of 118 grs of 2F powder for the .50 and 109 gas for the .44-90 might have held the wad under the powder tighter creating back pressure, I don't know for sure. The problem stopped.