We’re having an issue where the VrayDisplacementMod stops subdividing when an object is moved via a point cache far away from 0.0. This also happens if you move an object far away using an objects sub object selection so that the pivot still remains at 0.0.
This may be consistent with a larger Max issue where units get buggy when far from 0. Many things, including simply moving an object will begin to snap in big increments while moving …for no reason except the scene bounding box is too large or far away from 0,0,0. Perhaps the units are getting blown out at that distance and making it not work. I ran into this myself while making a 2-Mile long facility. The only fix was to change units or scale everything down. The “large scale scene” issue is fairly well documented throughout forums if you wanted to dig further.
But I am not a programmer, so it may in fact not be related… Just a thought that may help troubleshoot.
@DaveKW What if you merge the object into a scene with larger SCENE units? For example use meter as SCENE units instead (and display units whatever you want, mm or cm)