I think I’ve resolved it. The labelled files are .lnk files pointing to directories and the target is on the mapped drive, which is just mapped on computer 1.
On computer 2, this drive is not mapped and I assume as DOpus can’t resolve that the .lnk points to a directory, it treats it as a file and just moves the .lnk to the top of the file-list, but not above folders. (And as I have intentionally set Mixing to “Folders listed before files”, it seems it doesn’t work correctly.)