I'm on the newest snapshot of Java edition, unmodded server, and my friends and I followed an Ocean Explorer map to a monument. However, when we got there, it was all one big dark room. We mined out the roof and there was no elder guardian at the top. We mined out the side wings and there were no hallways or rooms. The ENTIRE ocean monument is just one dark room with nothing inside it and no sea lanterns to light things up. Our disappointment is immeasurable. 

Seed is 8593712711510346333 and coordinates are in one of the screenshots