I offer details that argue against the problem being caused by an upgrade to the Messages app:
4/5/2018 (VMA.Client.exe) Verizon Messages 18.104.22.168 on Windows 10 from Microsoft Store
9/10/2015 (WinVMAClient.exe) Message+ 22.214.171.124 on Windows 7 (old download)
BUT this failure began after 19 July 2019 for both my versions.
Evidence (mine and others') point to Verizon having changed something in their server(s) environment without providing an update for Messages for all OS platforms.
Completely out of our control!