We have 5 of them. 4 are ortho imagery and 1 is a hydro base layer made from NHD vector data.
They are compact tile caches made on arc 10.3.1 desktop with the Manage Tile Cache tool:
After the caches were made we copied them to a local drive on the server (trying to get the best performance out of them). Then we added the 4 ortho ones to a mxd and published. The hydro was added to it's own mxd and published. I also created a test service from one of the ortho caches today with the same result.
Lastly, yesterday I discovered that they are not printing in our Geocortex site, but are displaying fine. Not sure if this is a related problem.