Hello Mark
I have been informing you about this many many times and there is something really odd with your hosting or there is some cleanup service running on the site. This is not the first time this has happened on your site, there is some cleanup service running that is emptying the contents of your temporary folder.
I have done a lot of experimenting with Cache on my site, and I am sorry if I caused you any grief or wasted your time.
I think the most likely culprit is:
https://www.regularlabs.com/extensions/cachecleaner
Whatever is going on this problem got worse after attempting to upgrade from Joomla 3.8.13 to 3.9
Throwing the following error
Could not open archive part file /home/finalb9/public_html/tmp/Joomla_3.8.13-Stable-Update_Package.zip for reading. Check that the file exists, is readable by the web server and is not in a directory made out of reach by chroot, open_basedir restrictions or any other restriction put in place by your host."
If we are talking about the same thing I have only been aware of the potential cause of the problem since mid-December.
Probably not that there is anything wrong with "cache cleaner" as such rather that I have it incorrectly configured.
I am asking Peter van Westen about this now with a view to avoiding this in the future and I will update here.
I just spent the past 2 hours trying to figure this out and this is really taxing.
Again my apologies.
Anyway, it is now updated to the latest 3.0.2, and if you still experience issue with your other thread, please update the other thread.
Thank you I will double check that everything is working properly and update the other thread accordingly.
all the best
Paul