Import MIDI files into Cubase via USB from Yamaha SX900

Hi. This is a bit of a specialist question about how to import MIDI files into Cubase from a keyboard (I have a Yamaha SX900) via USB. Yamaha say this is the only way to transfer all the data into Cubase from one of their keyboards - and I believe they own Steinberg; they certainly promote this as the standard way of working in their support videos.
It used to work fine, but now doesn’t.
Just to rewind a bit, the idea is that you record the full performance (all voices, styles, etc., etc.) on the keyboard’s 16 channels, then save on a USB stick on the keyboard, plug the memory stick into the PC and import into Cubase. As long as all the channels are pointing back at the keyboard, the imported data “plays” the keyboard voices, styles, etc. and it’s all fully editable in the usual way in Cubase once the data has been imported.
It used to work fine until I created the SX900 as an “external instrument” within Cubase (I have Cubase 12 Pro); now when I try to import the keyboard data from USB, it shows all the channels as instrument, rather then MIDI, and the voices, etc are all over the place.
For those who only use VSTs, etc within Cubase, this may seem like a strange way to work. But if you like to start your compositions as a “performance” on a keyboard, so you can hear it building as you play and then, once transferred to Cubase, you have all the benefits of tidying it up and adding extra voices, it’s great way to work - well, I think so.
My question is how do I get things back to how they were?! I suspect it may be to uninstall the SX900 as an external instrument, which I did so I could play direct into Cubase from the keyboard if I ever wanted to do that. Maybe the two can’t co-exist within Cubase. Or should I re-install Cubase from scratch?
My studio PC and keyboard are connected by both a direct USB lead and via a Focusrite external interface. I usually work through the interface.
Any thoughts, please?