In general, whenever this type of bug occurs, the problem can be solved by removing the cversati ctaining the problematic message. The following steps work the iPhone 6s and newer, excluding the iPhone SE:
- Force the closing of the iMessage applicati.
- Ask Siri to send an answer to the sender of the message so that the Unicode string is no lger the most recent speech bubble.
- 3D Tap the Messages applicati ic from the Home screen, then tap New message from the menu that opens.
- Tap Cancel in the upper right corner of the New Message screen.
- Tap Edit in the upper left corner of the cversati list.
- Tap the circle to the left of the cversati ctaining the problematic message. A blue check mark appears.
- Tap Delete in the lower right corner.
If you have an iPhone with Siri but not 3D Touch, ranging from the iPhone 4s to the iPhone 6 Plus and the iPhone SE, the steps are slightly different:  Forcing the closing the iMessage applicati.