1. Edit a cell off the coast
2. Fast travel there
3. Z-Fighting water

Doesn't happen approaching it on foot.

This seems suspiciously similar to large statics disappearing on fast travel, unless set to full LOD. I'm guessing the water is Z-fighting with the LOD water, inappropriately kept around. This is pointing to a general issue involving determining distance for purposes of LOD when fast traveling to objects in an esp.