Same Issue here, just found out it works when opening file using the UNC path but not when accessing via mapped drive.
I tried to remap the drive to see if that would now work and no luck but UNC path still works.
When I checked the info section of the file, Excel detects the file to have came from internet and does not identify the drive as full file path and location is just shown as drive letter e.g. U:>Folder name> instead of \server-name\Folder name
Any clue around how to fix this?