Noticed that a nearby chunk in the ocean wasn’t loaded properly, went closer to try to make it load and I noticed that all of the blocks have been changed to air from sea level to about y=-25. When I went to check it out I noticed it also happened in a similar fashion to the chunk diagonal of the affected chunk, but it didn’t go up to sea level. Look just beyond the waterfall to see the other affected chunk, which goes a little lower.

Vanilla, no addons or anything.