Random parameter changes on Ambika?

I am using the Ambika with Expert Sleeper’s Silent Way / ESX-8MD midi module, which is not 100% compatible with all synths. Typical issues are stuck notes / midi overload, however, ‘osc1 wave shape’ reverts back to ‘none’ on each re-trigger.

Generally, using the midi thru of another synth fixes any issues, but I can’t seem to fix this.
There are no modulations going on, and no other parameters are being changed.

Any idea what might be causing this?

If routing the MIDI Stream thru another Synth fixes the problem its looks like a signal integrity problem. My Ambika (as all MI Gar) works with all the Synths i have tested so far, so i guess the problem is more on the ESX-8MD Side but this doesn’t help.
You could try swapping the 6N137 for a similar one and hope for the best of tolerances, or exchange for some other Optocoupler (6N138 - but you need to change a Resistor, use the Forum search to find the Thread…)