Hopefully the issue has been solved.
The website owner disabled a plugin: wp-rocket
And changed the settings for a plugin (hellopack-shortpixel plugin).
So the image files in the tmp folder were no longer being generated again.
It was a wordpress plugin the problem, but it is interesting that it can just fill the tmp folder to such an extent and if the issue does not appear, I can believe that the storage was simply used with normal usage.