Hi @wpf848,
Here is a couple pages listing many of the restrictions.
They vary depending on the backend. OneDrive for Business is actually an interface on top of a bunch of different backends, which is probably one of the reasons why it is so quirky. I have actually seen that there is some odd behavior that is not listed, as well. Like this behavior:
I generally say that you should try to adhere to the most restrictive set they list, just to be safe. This means you should try to keep the overall path length below 250 chars and a single file name under 128 chars. I have seen some instances, however, where there were problems with paths even less that that…