Strange Multi-Turn Potentiometer Problem

[Yellow Eyes]

We're trying to get some feedback on the various motions our robot's arm can make and two of them use the 100K 10 turn pots (Bourns 3590s). One of them is returning what seems to be fairly normal values to the RC (for rotating the arm), but the other (for extending the arm) just sits at max (255 with a bit shift, 1023 without) no matter where you turn it until about 1/8 to 1/4 of a turn from the end when it suddenly sinks all the way down. When tested on a multimeter though, the values are normal, 0 to about 100K ohms. The 2 pots are connected to rc_ana_in02 (extending) and rc_ana_in12 (rotating). If we swap them, rotating continues to work, and extending continues to just sit at max. Has anyone ever come across this before? Or does anyone know any potential fixes?
Thanks ahead.