SSI fsize broken since server migration

Since the migration of my sites from inko to aldebaran, SSI “fsize” elements no longer work, while “include” elements still work:

It still works here however:

I tried changing fsize file to fsize virtual, and to give an absolute path, but nothing works.

Update: I’ve come a bit closer to the problem. I have an .htaccess in each directory to prevent hotlinking of archives. If I delete that .htaccess, the file size display works again.