Found a definite bug.
When the OP-1 is on a drum sound and you’re using Sketch as the sequencer, the device will lock up and spit out an error code when you are holding a key down, press the Sequencer button to turn off and then back on again; it then crashes when you release your finger from the key.
It doesn’t happen on Synth mode.
I’m running the latest firmware. (242)