The only thing I can think of is that the magenta dicrohic is slipping, are you going to white light and then back to filter in to focus your image ? or are you touching the magenta dial inbetween prints? If you are try not touching the dials and just make a couple of prints and see if you get two consistant prints.
Sometimes the dichroic filters are loose and any movevement on the head results in an inconsistent pattern of resulting exposures on paper. Colour paper (RA4) is highly sensitive to filtration changes.