I can’t pin down when exactly but we have upgraded our nextcloud application not too long ago and now having space slowly run down to now having 10GB free.
The area in question is /dev/mapper/nextcloud–vg-root/.
We have a different area for holding users files so I believe that it’s maybe logs or something similar taking up all the space. However, I’m unable to browse to that area in cli to see what is being used.
Is there anyone else that has had a similar issue?
First you can delete the backups for Nextcloud upgrades. Hopefully you a have a local backup for this. 
data/updater-****/backups
For big files and big directorys install the linux program ncdu.
ncdu /path
Maybe the previews of images need a lot of space. But i think you can not change it.
Really? Please check it out for for Nextcloud installation, “datadirectory” (config/config.php) and user directorys (“datadirectory”/username). Test with df, mount and ncdu. Post some details.
Thanks for your help. I used the ncdu program and was able to find where my space was going. It was in log files as I expected, but not related to the nextcloud software.