When playing a steady tone, Master meters are unstable, though audio is fine

I'm helping a friend get a system set up. When setting levels and gains using a steady sine wave, he noticed that the Master meters on the front panel "bounced" by one LED in a seemingly random maer. The audio is steady and doesn't follow the bouncing meters, nor does the Main meter in Universal Control exhibit this behavior. The "bouncing meters" are frequency dependent, being stable when the input frequency is above about 1.5 kHz, and at 50 Hz, the meters "bounce" by 3 or 4 LEDs. The input meters are stable. I haven't tried it with a digital input (no convenient source) but the "bouncing output meters" behave in the same way for all four analog inputs

It sounds OK, but this isn't much of a confidence builder.

Studio 192 Mobile

Serial number 16030028

Firmware DSP-V1.8-31

Windows 7 SP1 or Windows 10 (who knows what version) - two different computers

Coected through a USB 2 port, tried several ports all with the same behavior.