1) I uninstalled and re-installed the plugin, still doesn’t work
2) I don’t know how to verify that the google pagespeed DB tables exist in your database
3) disabling other plugins would be a bit too time-consuming, but those are the ones I have: Akismet, Better Search Replace, Contact Form 7, Envato WP Toolkit, Google Pagespeed Insights, Hello Dolly, Insert Headers and Footers, Jetpack by WP, Leverage Browser Caching Ninja, MailChimp for WP, MOJO Marketplace, Photo Gallery, PixthemeCustom, Regenerate Thumbnails, Remove query strings from static resources, Revolutions Slider, The Events Calendar, WooCommerce, WordPress Gzip Compression, WP Importer, WP Smush, WP Super Cache, WP-Sweep, WP deferred javaScript
4) I don’t understand your 3rd link’s explanation
5) I don’t understand your 4th link’s explanation