I’m not asking for a fix; just creating documentation of the issue for other users that may experience the same problem. I was able to solve this issue by only using IP Blacklist Cloud, or by only using Sucuri. Both plugins work just fine on their own with the other plugins in my installation, but not together. You can keep this marked as resolved.
Can the plugin author please reply to give us an idea of when the updated version of the Sucuri plugin will be tested with the latest version of WordPress? It has been nearly a week since the plugin update & we’re still seeing the compatibility warning.