Phantom Plymouth hard drive has suddenly apeared

I have something called "77 MB Volume" that has suddenly appeared this morning. It mimics the profile of an external hard drive. Most of the folders are empty. The README says:

This repository includes the ubuntu-core theme for plymouth.

Which tells me nothing. There is also a copyright file that references freedesktop, whose site I have not visited. Can anyone shed some light on this for me, please? Thanks.

Edit: It happened again today, but this time, it's a volume with 483 MB. So, with the answer from @AnonymousCoward987654321, knowing it was a deleted snap, I searched again here and found this: Suddenly a new mounted volume appears, how to remove it. I'd say that this finishes the puzzle.

Original research below.

Not really an answer I suppose, but I'm adding my own research here because I've got the same thing today. But before sharing everything I checked, I'd like to add that restarting made it go away. Anyway, here's everything I found out before that:

1. Hovering over the mounted volume, I could see the path (mountpoint): /media/<USER>/disk
2. Using df --all (or lsblk as suggested in the comments by @Serg), I found out it was loop6 (/dev/loop6)
3. Since it's new, I suppose (with a huge grain of salt) it could be related to updates. So I'm also sharing recent updates (with some anonymization on user and times). I believe if it's really related, it should be the newest, but it's possible it was there since yesterday and I just didn't notice before:

Start-Date: 2023-05-11  13:30:35
Commandline: apt -y full-upgrade
Requested-By: <USER> (<USERID>)
Upgrade:
 krb5-locales:amd64 (1.19.2-2ubuntu0.1, 1.19.2-2ubuntu0.2),
 libgssapi-krb5-2:amd64 (1.19.2-2ubuntu0.1, 1.19.2-2ubuntu0.2),
 libgssapi-krb5-2:i386 (1.19.2-2ubuntu0.1, 1.19.2-2ubuntu0.2),
 libkrb5support0:amd64 (1.19.2-2ubuntu0.1, 1.19.2-2ubuntu0.2),
 libkrb5support0:i386 (1.19.2-2ubuntu0.1, 1.19.2-2ubuntu0.2),
 libkrb5-3:amd64 (1.19.2-2ubuntu0.1, 1.19.2-2ubuntu0.2),
 libkrb5-3:i386 (1.19.2-2ubuntu0.1, 1.19.2-2ubuntu0.2),
 libk5crypto3:amd64 (1.19.2-2ubuntu0.1, 1.19.2-2ubuntu0.2),
 libk5crypto3:i386 (1.19.2-2ubuntu0.1, 1.19.2-2ubuntu0.2)
End-Date: 2023-05-11  13:30:37

Start-Date: 2023-05-12  19:00:12
Commandline: apt -y full-upgrade
Requested-By: <USER> (<USERID>)
Upgrade: code:amd64 (1.78.1-1683194560, 1.78.2-1683731010)
End-Date: 2023-05-12  19:00:24

Adding to that, running apt list --upgradable, I could check that those packages were not upgrading themselves, which could be related in some way (some pre-update check code that was not cleaning up after failing kinda thing?):

Listing... Done
gdm3/jammy-updates 42.0-1ubuntu7.22.04.2 amd64 [upgradable from: 42.0-1ubuntu7.22.04.1]
gir1.2-gdm-1.0/jammy-updates 42.0-1ubuntu7.22.04.2 amd64 [upgradable from: 42.0-1ubuntu7.22.04.1]
gnome-remote-desktop/jammy-updates 42.7-0ubuntu1 amd64 [upgradable from: 42.4-0ubuntu1]
intel-media-va-driver/jammy-updates 22.3.1+dfsg1-1ubuntu2 amd64 [upgradable from: 22.3.1+dfsg1-1ubuntu1]
libgdm1/jammy-updates 42.0-1ubuntu7.22.04.2 amd64 [upgradable from: 42.0-1ubuntu7.22.04.1]

I did end up installing/upgrading them manually, but with no apparent result.

I used the information user1695764 gave to find my 77mb volume was /dev/loop3.

Using the command "losetup --list /dev/loop3" showed it was mounted from a deleted snap (/var/lib/snapd/snaps/core22_634.snap).