This has been an ongoing issue with the 11.x, and now 12.10rc, firmware. If I have the "Trainer" sensor enabled (e.g. Wahoo Kickr), I don't get any pace information when running on the treadmill. Sent in a bug report several weeks ago, never heard anything back.
So far the only workaround I've come up with is to disable the trainer sensor when I'm not doing a "Bike Indoor" activity.