I have the same problem on my 1.13.2 server. There used to be tons of them around a coral reef way off shore, then one day I logged in and they were gone. I'm usually the only person on the server. Other mobs spawn just fine. The only time I see a few drowned is when a chunk loads for the first time since they get generated with the chunk. But if I go looking for them later, they've vanished. I upgraded this world from 1.13.1 at some point, but it doesn't correlate with when this started, so I don't know that it's related.
Andy Harrison
MC-195474
I have the same problem on my 1.13.2 server. There used to be tons of them around a coral reef way off shore, then one day I logged in and they were gone. I'm usually the only person on the server. Other mobs spawn just fine. The only time I see a few drowned is when a chunk loads for the first time since they get generated with the chunk. But if I go looking for them later, they've vanished. I upgraded this world from 1.13.1 at some point, but it doesn't correlate with when this started, so I don't know that it's related.
My mistake: when I press space (not enter), the UI closes.