Root ran out of drive space due to sync error

I found a situation on a NextCloud 11 install where root ran out of drive space as desktop clients synced data in root and not in the external storage.

Set-up, Ubuntu 16.04 LTS server + NextCloud 11 + High Capacity Raid 10 NTFS External Local Storage (boots NTFS through fstab). NextCloud is configured to store data only in the External Local Storage.

Through troubleshooting, as root superuser I did a -dh -sch command to see what consumed the root’s generous 80GB root space

root@server:~# du -sch /var/www/nextcloud/data/* | sort -rh
64G     total
35G     /var/www/nextcloud/data/user001
16G     /var/www/nextcloud/data/user002
14G     /var/www/nextcloud/data/user003
70M     /var/www/nextcloud/data/user004
39M     /var/www/nextcloud/data/user005
21M     /var/www/nextcloud/data/appdata_octpzo3i2o4i
3.4M    /var/www/nextcloud/data/nextcloud.log
516K    /var/www/nextcloud/data/files_external
0       /var/www/nextcloud/data/index.html

This returned that all the five users synced 64GB of data on the root folder instead of the external storage causing the nextcloud server to stall.

How can I remove this data so that I get access to NextCloud for further troubleshooting.

After some going around in circles, I managed to remove the files with the following as root (sudo -i)

rm -rf /var/www/nextcloud/data/user001/files/*
rm -rf /var/www/nextcloud/data/user002/files/*
rm -rf /var/www/nextcloud/data/user003/files/*
rm -rf /var/www/nextcloud/data/user004/files/*
rm -rf /var/www/nextcloud/data/user005/files/*

Now I may access the logs to try and find how the sync error generated.

Will update with more findings