I have just witnessed this bug for myself in my testing world on Xbox one, (Version 1.13.1) and I found a way to get them to stop floating in the air, and I hope this will give an insight into how to fix it.
I saw one of them floating and built a little platform underneath it and kept increasing it by a block each time. I had to raise it about 3 blocks, but a few times the Guardian took fall damage.
Now looking at the Guardian still bobbing up and down in the air, it was looking at one fixed position at all times, I eventually got it up to the correct level for it to head to the point it was fixed in trying to get to, and the moment it touched the water it started to jump around and swim around the room.
I then removed the platform (which I had used to get it higher) and shoved it back down the hole, to which it fell normally.
So, I think it might be that the A.I. gets confused when it leaves the water, and tries to head back (which explains why it always looks in a single fixed direction) and that giving it a platform to land on, or allowing it to reach a bit of water (to potentially "reset" the A.I.'s pathfinding) fixes the issue temporarily.
Hope this helps you figure out whats up with this bug, and how to recreate some of the results
Thomas Marchant
I have just witnessed this bug for myself in my testing world on Xbox one, (Version 1.13.1) and I found a way to get them to stop floating in the air, and I hope this will give an insight into how to fix it.
I saw one of them floating and built a little platform underneath it and kept increasing it by a block each time. I had to raise it about 3 blocks, but a few times the Guardian took fall damage.
Now looking at the Guardian still bobbing up and down in the air, it was looking at one fixed position at all times, I eventually got it up to the correct level for it to head to the point it was fixed in trying to get to, and the moment it touched the water it started to jump around and swim around the room.
I then removed the platform (which I had used to get it higher) and shoved it back down the hole, to which it fell normally.
So, I think it might be that the A.I. gets confused when it leaves the water, and tries to head back (which explains why it always looks in a single fixed direction) and that giving it a platform to land on, or allowing it to reach a bit of water (to potentially "reset" the A.I.'s pathfinding) fixes the issue temporarily.
Hope this helps you figure out whats up with this bug, and how to recreate some of the results