My wife's Samsung galaxy 8+ has recently started doing this. When she sends a message it will be repeated sometimes for 3 hours on the recipient's phone. This happens randomly and doesn't appear to be one recipient.
VZ customer support has been no help.
I am going to "reset to factory default" the phone, but I suspect the problem is not with the phone.
@lpclay, Thank you for bringing this to our attention, and we understand how important this is. When did this begin? Have you made any recent chnages to the device settings/software? Share details.