Caching plugins not working in WordPress / JustHost

Hi there

I run several WordPress websites, 2 sharing the same account at JustHost.com. Until a few months ago, caching was working with the 2 with no problem at all. I tried out several plugins and settled for WP supercache & Hypercache for 2 the sites. Then sometime around end of July, I started getting some funny unexplained issues one particular day, in the middle of adding content, mostly around timeout errors. They talked of resource overuse & the like. This continued for a while.

That week, there were constant time-outs, which with time became less.

Now similar issues are rare. I did NOT remove anything from the 2 sites & have basically the same plugins & not much more content. There was no sudden change in any way on the sites one of which I had not touched for months that could be seen as the trigger.

I had changed absolutely nothing on the 2 sites for months, except occasional updates, but none around the day time the problems started. The webhost however maintained they made no server settings changes.

I noted that CACHING stopped functioning on both sites, although it never had a problem before.

I have tried uninstalling, reinstalling the caching plugins, disabling ALL plugins except the caching plugins, nothing helps, repeatedly
I tried other plugins, including Total cache, etc … went through the set up, something I never had a problem with before, … at the end never any caching plugin-related code in source code. Simply no caching.

In the case of Super cache, if I test the function, I consistently get the message

The pages do not match! Timestamps differ or were not found!

I have no problem with exactly the same plugins on other shared hosts-servers where they work for a number of sites, like they did here BEFORE July.

I have had quite angry arguments with the web host support, because they claim they have done nothing to the server-settings & that I should contact the plugin authors, where they claim the problems must be or with my settings.

I have requested them to try installing the plugins themselves to help identify the source of the problem, but they say that’s is not their job.

I have no reason to believe the problem is with the DIFFERENT caching plugins, which cannot have stopped working simultaneously, Total Cache, Supercache, Hypercache, etc.

My question is, what could be causing this in case the Justhost support is right? What more can I do if even disabling ALL OTHER PLUGINS does not help????

In case it is server settings, what exactly on a shared server can prevent the above plugins from working?

Any help/clarification would very much be appreciated.

Regards