To be precise, I don’t use MIDI Maps, but I have to create the devices in the MIDI Device mapper, don’t I? So I create the devices and use MIDI-Out CHOPs triggered via Python to send the MIDI-Messages.
TD is sending out CC121 on all channels according to Cubase’s MIDI-Monitor. I have checked every device in the network, these are definitely coming from TD. I now use a pretty weird workaround by sending MIDI to Bome MIDI Translator Pro and “swallowing” CC121 from the MIDI-Stream coming from TD, which solved the problem for me for now. (this also shows that it’s clearly coming from TD).
Also, my patch (which is a touchscreen-controller for Cubase) hasn’t changed since about a year, and the problem just appeared a few weeks ago. Same PC, same TD version, same patch. I only updated Windows.