Try looking for Dual Messenger under advanced features. If you see a copy of the Messages app, then that's probably why you have 2.
If that the case to fix it you simply need to tap on the vertical 3 dot menu button and press Delete all my data to get rid of the clone. Or just toggle it off
This is a confirmed bug by the latest update of Google messages affecting both Samsung and Pixel phones. Guess we'll just have to wait for the next update.
