Interesting, thought I was at the latest but do see the version 1.9.10 driver:

https://usa.yamaha.com/support/updates/yamaha_steinberg_usb_driver_v1_9_10_for_win.html

V1.9.9 to V1.9.10
- Solved a problem in which noise may occur in a certain environment.

- Solved a problem in which a certain DAW software would terminate abnormally when switching the sample rate setting.

The usual checklist is:

1) Make sure your Montage is configured as USB MIDI mode (and not 5-pin DIN MIDI mode). If you see an icon at the top of your touchscreen that looks like a circle with dots - that's wrong. If you see an icon that looks like a sideways trident - that's the USB sig logo and indicates you have Montage in the right mode.
[UTILITY] "Settings" -> "MIDI I/O" under "MIDI IN/OUT" should be set to "USB" and not "MIDI"
2) Ensure you are using a USB 2.0 cable. Cable should be plugged into the square-ish USB connector on Montage labeled "USB to Host" and a rectangle-type connector on the PC (standard USB port you'd plug a flash/thumb drive into)
3) Don't use a USB hub or anything between.
4) If already using this config/cable, try a different cable
... possibly "you've gone too far, turnaround" steps below:
5) Check device manager - make sure Yamaha Steinberg USB drivers are reporting as operational
6) Start disabling other possibly conflicting devices (other MIDI/sound devices).

Turns out the problem was with my keyboard itself, as it wasn't up to date with the latest update (1.51)

Thanks.