I have had this issue for at least a year, probably two. Sometimes it works and syncs fine, all the messages are the same across devices. Other times some messages sent on the Windows 10 app don't show on my phone and some sent from my phone don't show on the Windows 10 app. Today seems even worse where most of the phone messages are not syncing with the app and vice versa. I tried reinstalling the Windows 10 app and no luck.
I reported the problem today as well. I don't see anything from customer support indicating that they are working on the problem.
I was told in a phone call from Verizon Tech Support that they know there is a problem, a recent Windows update broke Verizon Messages for Windows 10. A team is "working on it", but, I was told that Verizon no longer supports Verizon Messages for Windows 10. The only way Verizon supports for a customer to access text messages while using Windows 10 is to use a browser to visit the My Verizon webpage and see and send texts there.
This is clearly not OK, but I can't find any real support at Verizon to get the app working again.
@vzw_customer_support I would like someone from Verizon Tech Support to explain how 'a Windows update broke the desktop Verizon Messages app'. It continues to work for me, keeping messages from some users synchronized but others not. If it was a Windows update that caused the problem, wouldn't messages to/from ALL contacts be affected, NOT JUST SOME and SAME ONES? Explain the cause and/or how the synchronization is supposed to happen, PLEASE!!! It sure seems like there is something going on with the actual messages (or where they are coming from) to be synchronized that Verizon is handling properly.
from Verizon support today: " I was able to confirm that the Message+ Verizon Messages - Windows Desktop application is not compatible with Windows 10 computers. " No estimated time for remediation.
If it was actually important to Verizon, it would have been fixed by now. Thousands of complaints over dozens of threads... and that's just the people who are annoyed enough to complain. The Windows app doesn't work.