We've dug into it deeper and the issue appears to be the scrollbar on windows like Invoice (General Journal, Sales Receipt, etc). The center table, where you enter items, always has a scrollbar visible, even if there are not enough items to allow for scrolling. In Sierra when that occurs just mousing over the scrollbar will result in a crash. In previous OSs it didn't.
We have a fix and will push it out ASAP. In the meantime, avoid moving the mouse over the scrollbar in those window (unless you really need to scroll) and you should be able to limp along.