I have the same problem - only worse. Message+ has worked fine on my Windows 10 computers. A couple days ago (somewhere around 8/20/2019) it stopped sending or recieving messages. It looks like it works and even says "sent" on the bottom of my outgoing messages, but no one receives them.
I have no idea how many immportant messages I thought I was sending out went nowhere.
It stopped receiving messagfes at the same tiem (Iassume)
Messagiong still works fine on my Andoid phone and older Android tablet. Needless to say, the Android devices do not show the messages I thought I had sent from the computers..