The plugin seems to stop working when some condition is met. I have had to completely uninstall, and re-install it 3 or 4 times.
I set up all the minify and caching settings, checking as I go, then all the features just stop working. No minification or caching.
The only fix seems to be removing it, deleting the configuration file, and setting it up all over again, only to have it stop working again.