'Your storage is almost full' on Box (Snap)

My Snap Nextcloud is all up to date on my Box

I was getting a warning about lack of space, but only had 570 GB data on the 1TB disk: ‘570 of 610 GB used’

I worked out how to do the following:

To clear versions:
sudo nextcloud.occ versions:cleanup

To clear trash (in the GUI it wouldn’t get rid of the folders/files for some reason):
sudo nextcloud.occ trashbin:cleanup

To clean up uploads folder:
/var/snap/nextcloud/common/nextcloud/data/[user]/uploads

The uploads folder directly gets filled when the client is uploading files. When the upload finishes this folder gets cleaned out automatically. If one is absolutely certain that no clients for a particular users are uploading files then it is okay to delete the contents of the uploads folder.

Each of those gave me significant savings (in total 250 GB)

That’s all much better but still it says that I have ‘570 of 856 GB used’

OK, that’s much better but where is the missing 144 GB from the 1TB being used?

I have set my limit to 1TB & I am the only user

Anybody help me, please?

EDIT:
Using ncdu (which is great!) I get the below that seems to tell me that I am only using 570 GB on the whole system?
Further exploration shows that 99.9% of this 570 GB is in /var/snap/nextcloud/common/nextcloud/data

ncdu 1.11 ~ Use the arrow keys to navigate, press ? for help
— / --------------------------------------------------------------------------
580.0 GiB [ 99.4%] /var
2.4 GiB [ 0.4%] /snap
672.4 MiB [ 0.1%] /usr
365.0 MiB [ 0.1%] /lib
70.7 MiB [ 0.0%] /boot
13.8 MiB [ 0.0%] /run
10.3 MiB [ 0.0%] /bin
8.2 MiB [ 0.0%] /sbin
6.5 MiB [ 0.0%] /etc
2.2 MiB [ 0.0%] /home
1.3 MiB [ 0.0%] /opt
204.0 KiB [ 0.0%] /tmp
192.0 KiB [ 0.0%] /root
e 16.0 KiB [ 0.0%] /lost+found
e 4.0 KiB [ 0.0%] /srv
e 4.0 KiB [ 0.0%] /mnt
e 4.0 KiB [ 0.0%] /media
0.0 B [ 0.0%] /sys
. 0.0 B [ 0.0%] /proc
0.0 B [ 0.0%] /dev
@ 0.0 B [ 0.0%] initrd.img
@ 0.0 B [ 0.0%] vmlinuz