The example file has a really large embedded picture, it's 3MB which breaks Windows Explorer.
If you remove it or resize it from within Mp3tag (e.g., via Adjust Cover), the preoccupied space is still left as padding (which is reserved space for future changes). Unfortunately, it might be still too large for Explorer to handle.
Before you ask: removal of padding (or at least resizing it to something that makes sense) is on my internal list of things to improve for Mp3tag. Until then, you can create this workaround using metaflac.exe (you can download it from the FLAC website, look for flac-1.4.2-win.zip).
In Mp3tag, define a user-defined tool via Options → Tools, and name it, e.g., FLAC remove padding, put the path to metaflac.exe and use the parameters
--remove --block-type=PADDING --dont-use-padding "%_path%"
If you want to remove the embedded cover and the padding in one go, the parameters are
--remove --block-type=PICTURE,PADDING --dont-use-padding "%_path%"
This will also delete any cover from the file.
You can then apply the user-defined tool from the right-click context menu of the selected file in Mp3tag.