Another thing I have tried, that may give a hint about the interpreter issue, is a proxy function: https://github.com/EmmanuelP/root-test/commit/f66078f85ef0a2fb731bb9a5f5c0df21136e5bbd
But this test failed with the following error after a click on the menu item:
IncrementalExecutor::executeFunction: symbol '_Z16URZoomAllXAsLastP7TObject' unresolved while linking [cling interface function]!
You are probably missing the definition of URZoomAllXAsLast(TObject*)
Maybe you need to load the corresponding shared library?