I am not sure if my situation is close enough to yours to be useful, but here is what I can offer. We have been shooting LF the same amount of time. You know I shoot 7x17, mostly in the horizontal position. I have a dozen holders from AWB, early S&S, more recent S&S, Great Plains, early Lotus, brand new Lotus, and one of unknown parentage. With the exception of lens flare from shooting too close into the sun with an single coated lens, I have not seen exposure across the whole 7 inch side other than the notches.
The two Lotus holders are so new I have not shot them yet. I just tried to load multiple sheets in the Lotus. The first sheet went in fine. With the first sheet in place, the second sheet began to bind a ¼ of the way in and would not go beyond half loaded. Thinking there might be some variation in film thickness I tried this with one year old T Max 400 and older unnamed Photo Warehouse ASA 125 that was thought to be Ilford. The results were the same. Is there anything else I can check that would help?