Having made a few posts as well as searching for a few similar posts in the forum I have found the W3 team never respond to anything
I have used the plugin since December but my site was getting progressively slower, needing constant restarts.
it got to the point where it would white screen and need a restart daily with ram usage going up to 1gb (instead of the usual 300-500mb it is on my vps hosting a couple of sites) and it was clear there was some form of memory leak
not to mention the constant minify error that was emailing me and notifying me hundreds of times a day that 2 years ago someone from W3 said they would fix in the next release yet it still isn't.
deactivating the plugin made the white screen errors go away and each page load (including all pictures) in 1 second or less instead of the 3-7 seconds it was taking with the plugin switched on.
chaching is supposed to speed up your site but it slowed down mine.
throw in the need for constant restarts, the lack of any customer support (even for premium usuers) and site down time it is pointless using this plugin