Comment 9 for bug 1795668

I've also encountered the same trouble with some of my external thumbnailers (lo-thumbnailer, msoffice-thumbnailer, ...).

I realised that bwarp calls fail under Ubuntu and Debian because of --symlink options used on /bin and /sbin. --ro-bind should be used instead of --symlink.

Till problem is solved on the Nautilus side, I've written a small article to explain how to get back external thumbnailers under 18.04 and 18.10 with the help of a bwrap wrapper under /usr/local/bin.

http://bernaerts.dyndns.org/linux/360-ubuntu-nautilus-external-thumbnailer-failure

Hope it helps