Did some further testing today with a signal generator. It was wired as a source rather than sink, but I could easily repeat the glitches and sudden jumps by changing the frequency of the pulse signal (say from 1Hz to 2Hz). This is similar to generating pulses via tactile switch and seems consistent with what I've seen before. Constant pulse generation (similar to hold the tactile switch) from the pulse generator shows a pretty smooth action.

I think I've tried everything I could and I'm waiting for a reply from Leadshine.

Regards,
T.