Won’t show my changes until I deactivate plugin

FVM doesn’t do page caching, so it’s not responsible for the content not changing.
Deactivating the plugin, will likely trigger a cache purge somewhere else, that’s why it looks like it’s related. Did you try disabling any other plugin and see if the same happens?

It’s likely you either have some other cache plugin somewhere, or your hosting has some sort of page caching going on. You can ask them if there is any sort of cache enabled.

In regard of js/css file changes, those will obviously be cached (but not the page contents, just the css and js code) until you purge them. After all, that is the purpose of the plugin, to merge, minify and cache css and js files.

If you edit css and js files directly, you need to purge all caches available to you. That’s how development works.