Terrain following require internet?

I was out in the field today testing terrain following and ran into a problem. I load a waypoint file created with terrain selected, but as soon as the copter is connected my choice of relative absolute and terrain disappear. I get a was if I want to load the mission in absolute. Yea, that’s not going to work so well unless it was a submarine lol! Is it just a glitch in MP or is it an internet issue. As soon as I connected my laptop to a cell router, everything worked. But there’s a lot of locations that don’t have cell coverage I’m flying in the next few weeks. I though prefetching would also load the terrain grid data. Ideas?