What makes WP Super cache & all other plugins on a server fail to work?

Hi there

Up to around end of July 2015 all was OK with 2 separate sites sharing same account at JustHost.com. Suddenly, though several caching plugins, including Total Cache, Hypercache & WP Super Cache inexplicably ceased working, although they (I had settled for Super cache & Hypercache) did before on the same sites for over a year.

I have tried several times to ask them to at least look into the issue suspecting some server settings, but different guys have practically rubbished my observation/request saying their server settings are OK & the problem must be with the plugins! I had changed nothing b4 that at that time & the same plugins worked with no problem.
Now NOTHING, whether disabling ALL other plugins, or a fresh installation gets any of them to work. They simply do not cache.

No one in the respective plugin forums has a similar issue & I could not also get any suggestion of a possible server settings requirement may be removed or changed that may be responsible, making me give up.

The same plugins on other sites I run hosted elsewhere work with no hitch.

I have never removed the 2 plugins from the 2 respective sites, but have them deactivated.

In the case of WP Supercache, there is a simple test provided to check after installation if caching is working & consistently always get these results, just like after I re-enabled the plugin again a few moments ago:

Fetching http://www.site.com/ to prime cache: OK
Fetching first copy of http://www.site.com/: OK (1.html)
Fetching second copy of http://www.site.com/: OK (2.html)
The pages do not match! Timestamps differ or were not found!
….

Between writing the last sentence above & this, I went to another site I am working on, hosted elsewhere & I installed WP Super cache. Within only a minute needed to set it up, ALL the above results with similar settings where => OK, with the time stamps similar.

As said, after the above issue started, I tried & interchanged the plugins & tried out Total cache a well, etc … so that for each site I tried out something else, but all ultimately they ALL do not cache. I had at the time they worked settled for WP Supercache for one & the other Hypercache.

Right now in the process of writing this WP Super cache has been activated, no sign of timestamp, etc.

I would appreciate if the developer or someone who may know could say, what on a server, where I suspect the problem to be is imperative for ALL caching plugins, including Super cache to work at all, so I may probably present it to the web host. I have no reason to think the problem is on the 2 sites, where ALL caching plugins worked before, but now dont. Now even disabling ALL other plugins does not make any of the caching plugins work.

Thank you in advance

Kind regards

https://wordpress.org/plugins/wp-super-cache/