If you look at the 'remote name' of the fields you are using on any of your sheets, are they the same in the old and new cubes?
They may look like they have the same name but perhaps the structure of the cube (dimension/hierarchies) changed slightly? If both are the same, I'd suggest contacting Tableau support! Replacing a cube data source worked fine on my side, but the remote names are the same.
Hope this helps!
Much appreciated the helps, i will check for the change in Remote name if any.