Might not be the sollution but when we did an upgrade from Mx8 to Mx9 we encountered that some OData services where broken and gave a similair error. The problem was when you had read access of a reference to another entity but you did not have access at all on that other entity. Sollution was to either remove the read rights of that reference or give access to that other entity.
But I still do not know if this is a feature or a bug. You could argue both ways.
Regards,
Ronald