XTouch Pan/Surround Control

I've been using my Behringer Xtouch control surface for a few years now to control Logic, and it works pretty well. But a while ago for reasons I can't figure out, I can no longer use the rotary controls at the top of channel strips to control pan/surround, even though "Pan/Surround" is selected under "Encoder Assign." The controllers work for all the other settings: track volume, EQ, Send level, etc. But it just stopped working for pan, which is the one function I actually want them to control.

Any ideas as to why the knobs would have stopped working to control pan?