Working with a slack (sticky) sourdough
As you know, as the bread proves a matrix of bubbles is formed. And just like blowing soap bubbles, the bigger they get the more fragile the bubbles are.

When you bake in pans you can let bread rise a lot as long as you are gentle when you move them into the oven. If you are using bannetons, you can’t let it get so fragile and still survive being turned out. All that happened was that lots of your bubbles broke, and some joined up to make the bigger less structurally robust large holes. 

So you got plenty of rise, you just inadvertently knocked the bread back. I’d suggest shortening the final rise.