What happened
I was flying around in creative mode when I noticed that the Guardians were not swimming normally. I went to three different Ocean monuments and noticed the same thing at all three of them. The guardians all had bubbles around them and were suspended in place in the water. They normally don't have the bubbles around them when sitting in one place relaxing so I knew something was wrong. Note that I was using Experimental mode on the world.

What I expected to happen
I expected to go to the Ocean monument and see the Guardians around the monument swimming normally and with more activity.

Edit: they can swim up but not very far. And cannot swim while using their laser beams. When you first discover a ocean Monument they all go to the bottom.