Back lever gives me acid reflux

Title says it all.

Anyone have this problem, or know what the problem is?

With acid reflux or back lever instigating it.

One of my guys who has GERD, cannot go inverted or horizontal when it acts up.

Seems like it's pretty clear that doing inverted hanging type stuff could easily exacerbate an existing problem. Up to you what you want to do about it but generally it's either proton pump inhibitors such as omeprazol or H2-inhibitors like ranitidin or pretty extensive surgery in some severe cases. Occasionally you might find an ulcer in which case you might be helped in other ways such as antibiotics, but reflux disease without any sort of gastric or duodenal ulcer is quite common.

I'm fine when I'm inverted. It's just when I go into the back lever, I get an acid reflux feeling in my esophagus.