This is sometimes caused by stale messages on your device, prior to the EA.
You can connect to DM and click backup/restore. From there, select advanced. The right side window will show what is on your device. Scroll down to messages, and click clear. This is not selective however, and will remove all messages, not just the ones you aren't able to delete on the device.
Treat your password like your toothbrush. Don't let anybody else use it, and get a new one every six months.