Can't load chat widget since installing Defender

Since I Installed Defender, the chat widget won't load and I'm seeing the following error:

Failed to load resource: the server responded with a status of 403 (Forbidden)
wpmudev-chat.js?ver=2.2:9 init: error HTTP Status[403] Forbidden
ytprefs.min.js?ver=4.7.2:7 YT API init

When I disable 'Prevent PHP execution', then everything loads fine.