Here a a few dumb questions.
Any change in Powder lot? Primer lot? Bullet lot?
Is this the new brass you just got? How does it compare in weight & capacity to the first batch you used? Have they been properly trimmed?
Any funny looking marks on you case after extraction?
I just can't see fouling causing pressure problems. Sure would make it shoot like crap; but excess pressure?
A lot of redundant questions I know.
Just rambling off the top of my head.