Couldn’t enable Mod Assign mode just now, as if I never pressed the button.
Just before that, in the same session, the HOLD switches would enable, but they wouldn’t hold any notes.
My normal morning ritual is to power up the Gemini, ignore whatever is selected, enable Init mode for both layers (lower, than upper) and do the work in the upper layer, in Single mode. I tweaked some parameters, and then had the two problems above.
I tried Hold mode in the lower layer, and it too would enable, but not hold any notes.
Repeated the whole thing after power cycling the Gemini, but now of course all worked as expected. 