This question already has an answer here:
All of sudden I noticed two new disks in my Ubuntu 16.04:
/var/lib/snapd/snaps/core_5662.snap (deleted) and
/var/lib/snapd/snaps/chromium_506.snap (deleted) .
What are they and why did they appear?
The first disk appeared several days ago. I noticed the second disk only today and shortly after that my Chromium crashed and all bookmarks and browsing history for the last 3 months disappeared. The new disks do not seem to have any Bookmarks files though.
Disks utility does not show any changes to the original actual disks. It looks as if someone has mounted two additional disks.