I see it on occasion as well. It's an artifact of running two amps with the "alternate channel mapping" with auto-adjust to noise enabled.
With one amp and normal channel mapping, auto-adjust to noise could adjust each channel's threshold individually. Now, with two amps and alternate channel mapping, channels A and B thresholds of each amp must be adjusted together. If the auto-adjust can't adjust the relative gain of one channel by moving the threshold to the target value (as it is constrained by the shared thresholds), the error message is shown. It's part of the compromise I mentioned. It is normal behavior, with the current firmware.
Don
WD9DMP