The board would completely disengage and the nose would drop. The best I can explain the feeling is that it felt like I’d go from tapping the gas to pushing the clutch all the way down. There would be no ‘pushback’ from the board beforehand. Sometimes it’d happen even when starting from a standstill.
From what I remember, the blue power light would be on, but it would take restarting the board for it to engage properly again.