Hi Courtney,
This is an issue in Mendix which was fixed with the 7.14.1 release - check the relase notes - https://docs.mendix.com/releasenotes/desktop-modeler/7.14
When the XPath constraint of a reference selector, reference set selector, or input reference set selector contained more than one occurrence of '[%CurrentObject%]', they were not resolved correctly, leading to no objects being found. All occurrences of '[%CurrentObject%]' are now resolved correctly. (Ticket 62713)
I dont think there is much you can do apart from upgrading.
-Andrej
There is no reason this would not work: I use this construction regularly. The most logical explanation is that there is either a data issue, or a security issue (e.g. Entity Access which is too tight).
I would suggest debugging by creating a microflow which retrieves every object in both paths, and then intersect the resulting lists. Then, place a breakpoint in the microflow, so you can inspect the results. If you have data after the intersect, you have a data security issue. If one of the lists is empty, you have a data issue.