This display problem is a problem in the editor and Ocean was drawn normally during the PIE.
When the problem occurred, we observed that only a part of the WaterInfoTexture in the WaterZone was written. Pressing the 'Force Update Water Info Texture' button did not improve the situation at that time.
This problem has not occurred for Lake, it works fine when placed away from the origin.
Issue reported in [Link Removed] by [Link Removed]
1. Create a new WorldPartition enabled level.
2. Add a landscape with a resolution of 4K to the created level.
3. Set the coordinates of the created landscape actor to (-4000, 96000, 100).
4. Add Ocean to the landscape. At this point Ocean is correctly displayed.
5. If you save everything and reopen the level, the Ocean will no longer be visible in the editor in the area away from the origin (see attached video).
6. If you move the Ocean in step 5, the display in the editor will be corrected, or if you save the level in that state and reopen it, the Ocean display in the editor will be incorrect.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-180925 in the post.