Semi - That is really cruddy stuff. It may be a PITA but maybe if you carried an extra ramrod or cleaning rod with you and put a breach scraper on it you could scrap all that stuff out before you loaded the next shot.
I never experienced anything like that. My first impression is that you left a charge in the rifle and it got all caked up in there during the cleaning. And maybe it would be true if you were a novice, but I know you better than that. I think anyway.