Can't edit or use Menu on Inserts in Record Mix Track

I’m running Nuendo 12 on a powerful well set up PC.
I have the Steinberg Multiband compressor as a Record Mix Insert.
When its first selected, I can edit the settings.
Subsequently neither the “e” effect edit, or the select arrow on the right of the insert will respond, but right click does. So, can remove, but can’t edit, or select another effect before the existing one is removed using right click.
This is ONLY happening on the Record Mix Channel. On the other channels, everything is fine.
Am I doing something fundamentally wrong ?? This feels more like a bug.

… could someone try to re-create this on their setup ?