I can't think of any other setting that would impact it beside their access levels and sharing. 

There is a backend setting that you might want to check, where you can set if resourcing should use the project schedule or the user's schedule. You'll want to set it to resource schedule. I can't recall if it's an option on a template vs a full system setting and I can't get into WF at the moment w...

Do they get an error? Or Is the page just blank? Have you checked their Workfront Access Levels to make sure they match?    You might have to open an Adobe support ticket so they can look at your system internally to see what is happening.     

could you share your filter that you are using on your report and maybe an example screenshot of a proofing workflow where the proof should not be on the report but still is?

The one I provided will look at the "parent" folder instead of the subfolder   Documents Section Final Files Folder (<-------this is what it will identify)  Sub Folder Sub Folder Sub Folder    

I would still have the system admin check their actual access levels in Workfront and make sure they have the same access level (not just license).  Access levels are customized versions of Licenses.   I would also double-check check the dashboard is shared with the user to have view access. I'm not...

https://experienceleague.adobe.com/en/docs/workfront/using/administration-and-setup/manage-groups/create-manage-subgroups/manage-subgroups#remove-a-subgroup-from-its-parent-group-and-make-it-a-top-level-group    

Try this instead.   EXISTS:a:$$EXISTSMOD=EXISTS EXISTS:a:$$OBJCODE=DOCFDR EXISTS:a:documents:ID=FIELD:ID EXISTS:a:parent:name=Final Files

what is your recommendation for sharing objects with small subset of users outside of the original shared list.   Example: Request Queue for Marketing is shared with the Marketing Group. However there are 3 users in the IT Group that can request items from marketing and need access to the queue. 

I use external lookups with control projects and custom forms to help manage extensive lists for drop-downs. I find that using a series of filters in the external lookup and custom forms on the tasks helps mitigate most issues.