Been having this issue since 1.0, entirely client-side, everything works fine for the host
Does NOT appear to be due to any form of latency or network issue. The exact same spots will be "desynced" every time we load up the same save.
On the surface it is most often only a "spotty shell" orbiting an area of terrain (As in the photo in OP). The "shell" can be dug through, but will pop back in after a few seconds. The terrain underneath can still be dug as normal.
Under the terrain there is the occasional large chunk of desynced terrain, all of which will respawn after a few seconds