Why won't Facebook Messenger show all notifications?

[AC Question]

I have a LG Volt on Virgin Mobile that I got about 8 months ago. Recently, I found that it doesn't notify me consistently of incoming Facebook messages. It sometimes shows a few messages, but for the most part I have to go into the app to see them. For example, whenever I get messages from group chats, the notification preview only shows a few of the messages that I received.

I'm pretty sure this problem started after I tried out Echo Notification Lockscreen, when I set for that app to manage notifications, but I don't know how to revert it.