Lost MIDI control in Cubase 12

[kritikon]

This is doing my head in - must be some setting in Cubase Artist 12 but buggered if I can find it.
For some reason I now can't use direct midi control in C12 from any keyboard.

VST plugins and connected midi synths will play recorded midi parts perfectly. When I open up a VST plugin in key editor I can click on the keyboard and play notes. I can draw in midi notes etc and get them to play back on plugins and synths. All of my keys show midi input activity on the little green meter down in the bottom right but won't actually play plugins or midi synths. In the Studio Setup->Midi Port Setup my midi ports show as active both in and out. All Midi Inputs is also ticked. All and any midi channels I try to use all have All Midi Inputs ticked.

I have my keyboards through a midi patchbay, and every keyboard does the same thing - they all show midi input activity on Cubase, and if I repatch them, they'll all play each other happily, so it's not the patchbay. I even tried changing the midi channels on a multitude of synths - all working, and the Cubase midi channels all match. If I open up Artist 10.5 everything works perfectly even on the same project so it has to be something in Cubase 12. I even reloaded my interface driver - still nothing, but 10.5 works perfectly. It can't be the new Win11, as Artist 10.5 works perfectly on it.

Any ideas? It simply has to be some obscure setting in 12 that for some reason has disconnected my midi keys from playing out. 10.5 works perfectly, 12 will play back recorded and plugin GUI keys (and drum maps etc) but I just can't use a keyboard to directly play anything. I can get work done by going back to 10.5 as the midi works perfectly with exactly the same setup, but I'd rather use 12 - no point having it if it won't let me play midi. Grrrrrrr

[skijumptoes]

You haven't got a global input transformer enabled? Actually, I don't know if it's in Artist - but it does have a project input transformer. Could be worth a check..
https://steinberg.help/cubase_artist/v1 ... mer_c.html

[kritikon]

I'll check that out - don't think so though. Pretty sure I've looked through the input transformers already.