Looks like you are dealing with MDI (Multiple Document Interface) child windows. The “MDIClient” parent window can spawn multiple “MDIchild” windows. UiPath sees the same selectors for all the MDIchild windows and uses index to differentiate windows which is unreliable.
In my case, the active MDIchild window, which was the on top, always had idx=‘1’. Fiddling with the index also didn’t help as it always seemed to work only on the topmost window.
@loginerror Any tips on dealing with MDIchild windows?