Large Bubbles, Just Underneath the Crust

One of my longstanding challenges with bread machine bread is the formation of very large bubbles just underneath the crust as the dough goes through long rise cycles. It happens by far the most on my sourdough bread, which is leavened with wild yeast only. The bread machine imposes many limitations, including the fact that it goes through all of the bread making steps in one continuous pass.

-> I understand that I can remove the dough from the bread machine, shape it, bake it on the stone in the oven, etc. Heck, I can use a mixer or make it by hand. I know it and enjoy it making bread those ways ... but ...

-> Suggesting that I do it "another way" is not going to help here. What I am trying to accomplish is to get the best bread possible from a programmable bread machine using its ordinary programmable cycles. I can adjust ingredients and set the timing for each step in the bread machine's cycle. With the sourdough recipe, another goal is to use only wild yeast and avoid commercial yeast. 

My current solution is to check the bread from time to time during the long rise cycles. I use a razor to cut the large bubbles during the rise. It works, and it works well, but they are annoying interruptions.

-> It would be better if I could understand the root cause of those large bubbles just under the crust and how to prevent them from forming in the first place. Large bubbles form elsewhere on some loaves, but not that much. The problem is most prominent anywhere on the top of the loaf. 

Any thoughts about the cause for topside large bubbles? My web searches have come up dry.