Resistance and Elevation not according to course in bike indoor

I often use the Bike Indoor feature on the Garmin Fenix 6X Pro Solar to ride a course on the Tacx Neo 2T.
Usually, it works in setting the resistance and elevation & climb according to the course chosen.
Unfortunately, it does no longer work. I have had that problem before, but it seemed to be resolved a couple of times, now it reappeared again.

So what I do.
1. Create a route
2. Load it to the watch
3. Use the Bike Indoor activity to reride it on the trainer.

What should happen in step three, that it takes the elevation etc. acc. to the route chosen.
Unfortunately, that a does not happen exactly (so there is a slight difference in Elevation starting point to the route (which wasn't there before).
It does then calculate a climb somehow, without changing the trainer's resistance to the grade.

Any way to overcome this or can this be fixed please?