In multiple locations the Ocean Monument will spawn but not be fully formed. The entire middle, or more, will be missing. Not sure if this is due to the chunk already being loaded and it being created since the 0.16 update, or if this is a standard issue. Only discovered 2 ocean monuments so far, but in both cases, the entire middle was missing leaving everything out in the open. No gold blocks or chests. Only one monument had a room partially filled with sponges as it was sliced in half to the open ocean.

Both monuments are a good distance from spawn, but realm has been active for months and possible someone had been in the area at some point previously.

Will try to grab a screen shot next time I encounter one, as the 2 found so far have been heavily modified while we were raiding it on the realm. Realm is not mine so unable to download to check it out.