I used lsblk to check connected devices, when I found that there are a total of 3 loop devices for the same snap "core", with revision numbers.
loop1 7:1 0 81.6M 1 loop /snap/core/4110
loop2 7:2 0 81.7M 1 loop /snap/core/4017
loop0 7:0 0 81.3M 1 loop /snap/core/3887
On checking the mount directory of snaps, this is what I get:
drwxr-xr-x 24 root root 321 Jan 22 13:17 3887
drwxr-xr-x 24 root root 321 Feb 6 20:48 4017
drwxr-xr-x 24 root root 321 Feb 20 22:37 4110
lrwxrwxrwx 1 root root 4 Feb 23 19:31 current -> 4110
and snap list shows this:
core 16-2.31.1 4110 canonical core
Why is snapd not removing the old versions of snap core? Is it a normal behavior, or is there any way to remove this if this is not supposed to happen? I'm using Ubuntu 16.04.