Do you mean that you have seen this for GPX or FIT files copied to the watch manually, not using routeCourse or another app? If so, does it matter if they are FIT or GPX?
Thanks.
It was when I transferred a TCX to the watch using Garmin's old Training Center app (which, I believe, converts the TCX to a FIT behind the scenes before doing the transfer)
Another 5X user has reported this too, and it seems to be a quirk of the Fenix 5X with some routes (possibly all, although the other user had mixed results).
We're sending the exact same FIT files to the Fenix 5X that we've been downloading to the routeCourse app since it was launched, and they work great on the other devices (including the Fenix 5 and 5S), so my current assumption is that this is a bug in the 5X firmware, but I am on the lookout for further information.
There appears to be a workaround though: if you go to the map from Navigation it does this but it you go into by choosing an Activity and using it as the course it's ok. (I may have those backwards, as I do not have a 5X myself to experiment with.)