I have used Message Plus for PC (not the Windows 'App' which gets horrible reviews), for many years, have uninstalled/reinstalled, verified sync settings, etc.  This is not my 'first rodeo.'

I use this on my Windows 10 Pro PC, used it on my prior Windows 7 PC, and use the Verizon Message+ App on my current Galaxy Note 8, Oreo.

Performance has *always* been inconsistent.  Sometimes texts are synced and shown on both devices, and sometimes they are not.  It is quite frustrating, and *not* the result of user error.

Verizon has not updated the PC App for several years now, and I would suspect that this is the reason for this, and other problems.  If Verizon "cared" about the user experience, they would update this app, and not just reply with the stock answers of uninstall/reinstall.

This is just a poor program for PC, and needs to be improved/updated, and this hasn't taken place for many years.

Sorry to vent, but these problems have been going on for quite some time now, with absolutely no changes or updates from Verizon.