Some channels on a 2100-M connected to a 2100-A16 jumped channels - ie the value that appeared on one line moves to another.

In this case a 2100-A16 was driving two 2100-Ms. One local and one a long distance away.
A cable fault had appeared on the cable to the second long distance 2100-M, this affected the local 2100-M clock and reset lines. After much changing of gear, the fault was isolated to the cable to the second 2100-M, when this cable was removed, the local 2100-M would work OK. A new cable was laid to the second 2100-M.