After updating to the newest version of Message+, I only receive notifications on my watch if the message I receive was sent via SMS. Messages received viat Chat don't show up anymore. I have a Pebble smartwatch that previously would show all messages I received, but now they'll only show up if they were sent as SMS. I was able to verify this because when my dad sent me a message, his send button said Chat under it and I never got a notification on my watch. One of my online accounts has an SMS authenticator attached to it, so when logging in to that online account with an SMS authenticator, I got the authentication SMS notification on my watch as well as the Message+ app.
Because they aren't sms. Android doesn't treat them the same. You'll also notice chat doesn't notify you on your car Bluetooth either. I assume Verizon was trying to implement their own version of imessage or hangouts but they failed badly to the point that many people are not getting messages anymore
When I get Facebook messages through Messenger they pop up on my watch, so I'd assume the same functionality is possible, but would need to be built into the app instead of relying on Android to do the notifying since it isn't SMS. I do agree that they took a step or two backwards, although I've only been with Verizon for a month. I liked the previous version of the Message+ app better.