I lost all ability to edit pages after Friday’s Fusion updates, on one of my sites only. All the sites are hosted by the same company, and this site was the newest and had the least information. Avada support suggested I increase some numbers in php.ini, but none of my other sites had those settings changed.
After 48 hours (before changing anything in php.ini), I became a little desperate and re-activated some plugins, including LightSpeed cache. Then I de-activated Fusion Builder and Fusion Core and re-activated them. Presto! The builder is back working properly.