Op-1 Volume Knob stopped working

Somehow, the volume knob on my Op1 stopped working. It does not feel mechanically damaged, still turns, but no change in output volume.

Anyone else seen this?

1 obv plug in headphones and take them out and try again
2 play something that goes to max level (say radio in), turn the knob all the way up, does the volume increase gradually at all? mine used to do that, I emailed TE, they said it’s normal.