WordPress multi-site plugins for network sites?
 

I'm using a few plugins on the multi-site that are not FOR multi-sites. When I activated them for the network, they did not work. However...

What I did was install them via the network admin, but did NOT activate for the entire network. Instead, by installing on the network admin, it made plugins available to each individual wp subdomain...and I was able to activate the plugins within each subdomain dashboard with no issues.

Do you think it's worth trying that with these cache plugins?

Maybe. When you install plugins local to the site (not network multisite), they often do work. It may work for the cache plugins. But on the MS, just do Hypercache, not DB-Cache.

W3 Total Cache is another one, but it has more resource use, and therefore doesn't do as much as the ones I suggest. But for MS, it's the best option. You may want to try that one on the one MS you have.

We'll work on your security next. It'll be several days.