Sounds like you were getting incomplete burning, which usually points to using too small a patch for the diameter of the ball you are shooting. The fact that the balls are hitting all over the place also suggests the wrong patch and ball combination is being used.
Since the RS was shooting fine, it sounds like you are fortunately getting enough fast ignition and pressure to OBTURATE the PRB enough to seal the barrel using RS. Its not occurring with whatever load you are using of the Schuetzen. I am assuming that you did not use a chronograph to test the two loads, so you have no idea what the powder charge is doing.
Understand that RS is a substitute. While the same volume of RS can be substituted for an equal volume of Black Powder, safely, you FIRST have to establish a good load with the Black Powder, before making the switch to the substitute powder. It does work the other way. It would help to know what powder charge you are using. Whatever it is, its not enough.
Cleaning between shots, I Repeat, is a SAFETY issue. You are not shooting an AR-15! You are shooting a muzzle loader, using black powder. IT HAS TO BE CLEANED of any burning ember between shots to avoid endangering YOU, and others around you. The fact that you have not been doing this kind of cleaning when shooting RS just indicates that you have been living on LUCK, or are so new to the sport, that you are slow in reloading enough, that any embers burn out before you pour down the next charge of powder. It may also be a function of RS having a much higher flashpoint.
Safety is not an issue to be debated. Its not something you choose to do or not to do depending on how you feel that day. Violate safety rules, and you will thrown off a firing line by range officers. Repeatedly violate them, and you usually can expect to be thrown out of clubs. Of course, what you do in your own back yard, or in the field is between you and God. I think I would be very embarrassed trying to explain to St. Peter why I am at his Gate early because I blew myself up loading my rifle. i certainly would not have to be there trying to explain how my gross negligence got someone else badly injured or killed.