interesting.
I think you need to post more information for any usefull ideas. It seems really counter intuitive, that there should be interference with ribbon cables, but not with individual cables (as they would probably be close together as well, right?
what are "all the sensors (those and others)" ? is there anything more going on than just those 3 sensors you mentioned?
How do you power your sensors?
Maybe you could post a picture of the connectors, both ends of the ribbon cable - I'd be interested in seeing it. I feel like its probably something really obvious, that went unnoticed, becouse its so obvious... you know what I mean.
good luck
p.