I have integrated Facebook Customer Plugin on one of our websites. I followed the instructions in the developer documentation. It is working fine when there is an active facebook session. However, the plugin does not appear at all when there is no active fb session. I might be missing something but I have no clue on what that is.
The solution for me was adding #xfbml=1&version=v2.12&autoLogAppEvents=1 after the xfbml.customerchat.js file like :
js.src = 'https://connect.facebook.net/en_US/sdk/xfbml.customerchat.js#xfbml=1&version=v2.12&autoLogAppEvents=1';