Right after I received the Android 7.0 Nougat update (From Marshmallow), my Message + app crashes, some times when I'm sending a message and other times when I'm opening the app.
I currently have version 6.4.1111 installed and I have rebooted my device on many occasions since the upgrade, it still routinely crashes. Yes I am sending the crash reports each time.
There may be some stored data for the app conflicting with the update. You may want to try going into your Application Manager in the settings, and clearing cached data for the Message+ app. If the problem persists after that, I'd try clearing data for the app as well.