Named the chaiOS message bug, the issue occurs when users receive a certain text message with what looks like undiscernable text. The Messages app then becomes unresponsive. Users will need to delete the entire conversation with the user to get the app back to working order.
If the software is iOS 11.2.5, Apple should also be officially releasing watchOS 4.2.2 and tvOS 11.2.5. Both of those updates apparently don’t offer any new features.