Looking at the console message in my website, it appears Facebook changed the SDK on January 8th but didn’t update its code to reflect.
##########################
# The CustomerChat plugin is no longer part of the main Facebook SDK.
# To continue using it please use the correct SDK URL,
# meaning replace sdk.js with sdk/xfbml.customerchat.js.
# For more details see https://developers.facebook.com/docs/messenger-platform/discovery/customer-chat-plugin/sdk
##########################
So I fixed mine by doing the following:
Replace the sdk in the file facebook-messenger-customer-chat.php
Lines 22 and 23 the original code with the following replace the following:
const URL_PREFIX = 'https://connect.facebook.net/en_US/sdk';
const URL_SUFFIX = '/xfbml.customerchat.js';
make sure to flush all your cache (cloudflare and any wp caching plugins).