Turns out European versions of excel default to semicolon for the field separator when exporting csv files. This is due to comma being used as the default numeric separator. I guess that makes sense, but the file format is comma separated values! Perhaps Lightburn can add an option for field separator in the variable text window, as Microsoft makes the change to the field separator either system wide, or buried 4 layers deep in menus.
Another option is to use LibreOffice, as it will always allow you to change the field separator on export, helpfully enough in the export window, rather that in an advanced regional control panel sub window.