Please pass this info to the programming team for Messages Plus.
I have been trying to use Your Phone on Windows 10 as a replacement for Messages Plus but with not much sucess. What I have found is that other apps (Mail, Photos, Feedback) suffer the same problem as Messages Plus. The problem seems to be that the Windows UWP system is suspending the execution of these apps almost right after opening. Once suspended, they can not keep syncing and are then useless.
The only way around this, I am told, is to recode as stand-alone program and make sure that the program is not suspended as the UWP apps all are. UWP is for apps that are not "realtime" in nature.
Take Messages Plus back to stand-alone please and the problems will be cured.
I don't want to hear from Support other than they passed this info to the programmers.