Make sure your Montage firmware is up-to-date (this will ensure your instrument should be behaving as Yamaha would expect).

But, in general, the "feel" of something is very personal - when triggering anything via MIDI your mileage can vary. The engineers and programmers spend time with response time... when you think about any electronic keyboard there is the travel of the Key from rest to the bottom of its movement, exactly where the sound comes on is a critical setting and one that has everything to do with how it "feels"

As you noted, playing on the Montage is the ideal way to ensure the feel (at least someone has labored over exactly how that response feels), when playing via MIDI, the mileage can (and often does) vary. I personally have no experience with the Nord as a controller. But if the response is quite different from when you are using the Motif XF as the external controller, well then you must look into the connection or the controller.

Hopefully, someone here with a similar rig can give you some feedback.

Looking for 8-PART performances to help with another issue - I did notice that the keyboard (even local) seemed sluggish. I didn't drill down to see if a power cycle fixed this issue - if there was something unique about the performance I was using - or if something was going on with my MIDI bus (which was only "hooked up" to validate MIDI traffic). The latency wasn't "bad" - I could still "handle" playing. It was on the edge of noticeable and a little a few ticks away from unusable.

Typically, I do not notice latency but also am working with generally 4-PART (or less) performances.

This doesn't exactly match with your experience unless I disconnect the MIDI connection (USB, to the computer) and see that doing so helps. Then there may be some form of a connection.

Probably best to try to reproduce using the S90XS since that's the most current Yamaha MIDI device I have to connect to Montage.

Share the stock preset performance you are using which best demonstrates the issue.

Any other settings? Are you using single MIDI channel mode? Because I wonder if your Nord only sends one MIDI channel - and many of the Piano performances require multiple channels to cover the bases and will not sound if the velocity is not matching.

... EDIT (additional info):

Note that if this is a MIDI channel issue (improper routing for the performance you are trying to play) - then you can reproduce the problem locally (local keyboard control) by:

0) First, if check your keyboard setup for MIDI mode = multi or single channel. If your mode is single-channel, then this is not the issue. No need to continue.
1) Turn Kbd Ctrl OFF for PART 1
2) SELECT PART 1 (you can touch PART 1 on the touch screen from HOME or use the "PART SELECT" button "1/1" aka Number A [1])
3) Play your local keyboard (mash down on white/black keys of your Montage) and see if this seems like a "sluggish" Nord.

What this does is simulate having an external controller that transmits only on MIDI channel 1 (PART 1 control only).

If so (Montage now seems sluggish like the Nord), AND assuming your Montage is setup for MIDI mode = multi chanel - then the issue is routing. Since many performances need to be invoked by multiple MIDI channels in order to get all of the velocity layers to activate when different velocity layers are spread across multiple PARTs. One way to remedy is to use single-channel MIDI mode. Another way to remedy is to use a multi-zone keyboard with at least the number of zones to match your performance PART count - and choose each zone to overlap across the full keyboard (of the external device = probably not Nord since I believe this keyboard is zone limited). Another option would be to stick a MIDI router between which takes care of replicating MIDI channels without the external controller needing zone support.

I'm not even sure if this (MIDI channel routing) is really your issue or not - but if it is, you have options.