Recently I was faced with the problem that a customer website running with the WordPress plugin Cachify was no longer delivering compressed pages. I was sure that this used to work and was therefore at a loss at first. At first I thought that it might have something to do with the use of OPCache, as I had activated this shortly before when I switched to PHP7 for this site.
Incidentally, the switch to PHP7 alone brings an enormous increase in performance. OPCache also makes the site twice as fast (in my case).
So OPCache was not the problem. And since a look at the cache directory on the server showed that Cachify was busy creating and saving HTML versions of the pages, the problem must have been there before. Since the pages saved in the cache directory were not loaded, it could only be the .htaccces that was not working. As the site had been switched to https some time previously, this came into focus as the cause. Google often helps in such cases and I found what I was looking for. Someone had the same problem and had already taken care of the matter and written a new customized .htaccess and kindly published it on github. Uploaded it and lo and behold – the cached pages are delivered again.