My LG Octane shows unread text message when I have read all of them. I can go in and view and it clears. It isn't the most recent I have to go all the way through to clear it and never do find the culprit. I think this is only happening fairly recently.
I understand your concerns. It must be frustrating to see an unread message notification when none is there. Changing the message view from time to contact has resolved this issue for others. Please try; I have included instructions below for your convenience.
Using the Internal Keypad:
1. Open the flip and press the Key [MENU].
2. Press Messaging.
3. Press the Left Soft Key [Settings].
4. Use the Directional Key to scroll to one of the settings and press the Key to select it.
Select Messages View and then select Contact to display messages by contact, in threads.
The above instructions (page 53) and other helpful information can be found in your LG Octane User Guide online.