Looks like they've turned off replying on "Message+ Windows PC app Broken", where there was a discussion up to a week ago. So I wil reply here, since it is still broken. My Windows app quit receiving messages a week ago. Verizon support on that other thread kept asking the same questions. So I will again reply with my details and experiments. I tried four different methods:
I sent a message from each device and had one incoming message. Each row in this table shows what device I sent from, then if the four devices received that message or not.
The other party got all four messages, no matter which device it came from.
This clearly shows that it is not my computer or the one app on my computer. It is interesting to note that Win 7 and Win 10 can talk to each other and the Browser, but not the phone. It's like the Win 7/10 are on one platform, the Phone on another, and they can't talk to each other, but the Browser can.
So the Browser works but being logged into the vzw account will kick you out after three minuntes of inactivity. Not good for texting.