Designs exported to .gps files from OptiSurface Designer V1.4.4 is seeing a huge difference in elevation when loaded to the Field Level II. It was off 180 ft. It wasn't too bad since it was still in the Field Level II range.
But there's another design I had to change the
elevation in OSD because it was off more than 300 ft and Field level
wouldn't accept such a difference.
I think the problem is due to the large elevation values. The Trimble .gps file is only designed to handle elevations up to 320 feet. Above that it can often work but can have problems. So I recommend you get your clients to start setting their MB elevations to 100 feet. You can do this in the Trimble Field Level's settings.