So when you said you did a "quick clean" and judging from your investigation it looks like you never pulled the breech and all you did was push the fouling down the bore and packed it against the breech plug. Yea I could see where that would cause an ignition problem. Especially with the fouling being dampened with whatever solution you used.
I guess your lesson learned is to take the couple extra minutes and remove the BP. I know its a pain in the butt. But look on the bright side. if you would have done it you likely would have a taxidermy bill!