Although my problem seemed to be more prevalent than Flook's.
The first hole I found:
Here's two videos of Flook mining in the non loaded part:
From there, walking forward about 20-30 blocks brings us to a bigger hole.
This one is about 5x the size of the first one.
And then there was a smaller hole in the water slightly south east of the biggest one. (I think that's where this one was, or it could actually be part of the bigger hole, if it is, I'm still looking east but the last hole is about this size.
The annoying thing is that the first hole is in the jungle so it's hard to spot if you're not looking for it, and even if you are it's easy to miss as there's a few hills and a big stone/dirt wall that looks like a non loaded chunk nearby. that's why I took photos of the map locations.
But the good thing is the biggest hole in the water is viewable just north of the village that Flook's farming/building in so it's easy to get to... if you've got a boat. It'll be annoying to try and dig down as it's right under the water so we may have to mine from the land which is probably 30-40 blocks south or build a tunnel starting from where I built the torch pillars.