It’s a standard installation. I ended up disabling the other plugins (only a handful and all popular and standard ones I’ve used in combination elsewhere), activating WP-Optimize (worked), then going through and activating each other one, expecting the conflicting plugin to not work, or to render WP-Optimize inactive, but, they all activated fine and WP-O is active and working. So perhaps the order mattered, but I don’t know.