Most probably it’s something related to your application. Have you managed to find the actual source of the disk usage? I’ll recommend you to try and find out what exactly is the cause.
Here are a few tips on how to pinpoint your troubles
Linux find a biggest files in /
sudo du -ha / | sort -n -r | head -n 20
It will show you top 20 of largest files in your /. Having said that, this command is quite heavy and it might take some time to execute.
Another good command to skip the directories and just search for big files is
find / -type f -printf "%s\t%p\n" | sort -n | tail -1
Another problem might be you are running out of inodes. You can check this with the following
If you are indeed running out of inodes, most probably your application is creating too much session files or temporary files which are never removed.