I'm pretty sure I encountered one of these bastards once in Puget Sound, of all places.
My family had a nice inboard bow rider pleasure boat, when I was a teenager. We used to pile it up with family and friends and go crabbing in Puget Sound. Put the boat into Lake Sammamish, go through the Montlake Cut to Lake Union, then through the Ballard Locks into Puget Sound.
Then we'd putter around the islands until we saw a nice, easily accessible beach. We'd drop the crab traps, and motor up to the shore, offload everyone and all the supplies, then my Dad and I would go back out to check the crab traps we'd set on the way in.
On one of these trips, I'm driving the boat (I'm about 15 and actually had my boat driving license before my car driving license!) as Dad is getting ready in the front of the boat to hook our first buoy.
When I swear a HOLE opened up in the ocean that was about 3x the length of our boat, and we DROPPED into the air, and SLAMMED into the bottom of this hole. Which quickly filled up, and lifted us back up to sea level.
It felt like we dropped 8-10 feet. It seemed to me like the horizon went away. I was standing, with one knee on the driver's seat, one hand on the wheel, and one on the throttle, in the standard "boat pulling up to a dock" pose.
My Dad was getting the pole hook ready in the bow of the boat, and putting on gloves, and not really watching the water. So he didn't see anything. He was just suddenly slammed down to the floor of the boat, and - when he got up again - we were back at sea level. He thought I'd hit something, but I told him what happened.
I know fluid is weird stuff and does weird things from time to time that may seem inexplicable... but are really just probability asserting itself.
I've always thought that I'd found a rogue hole, that day. No idea if they can even happen in waters like the Puget Sound, but I'm pretty sure probability caught up with me, and let itself be known.