UDO S6 Desktop.
Using the Mod Matrix (LFO 2 → Env-2R) seemed to work normally until I hit the patch button and lost the mod.
Subsequently the only way I could get the mod to work was to hit the Mode button a few times, then I would just start working as expected.
I’m not sure if I’m missing something and this is how it’s supposed to be, or if there’s a glitch.