Inline Editing in Classic List View - Not working!

My problem: I'm trying to give my managers access to edit a certain field via inline editing in Classic List Views, but they  are unable to. 

Some more info:

• The field is a custom picklist 
• I personally have been able to edit the field via inline editing in the same list view, but I have a different profile
•  Managers can even edit this picklist field directly from the Account page, but NOT via inline editing on the list view. 

Here's what I've tried:

• I've updated the list view to include a filter by record type
• The field IS on their page layout, with "Read only" unchecked
• They have system permissions (Mass edit from lists) to that edit the field
• There is no filter logic in the list view
• Marketing User is set to True on their User record

What's even more strange... They can see the little pencil icon (that would indicate that they can edit the field) when hovering over the field in the List View... but when they click on it, nothing happens! They're even able to edit OTHER custom picklist fields in that list view, but not the one I need/want them to be able to edit!

Please. Help! What am I missing?