The Black Dot Unicode bug was discovered last week but it has been receiving widespread attention in the Apple community recently. Multiple popular YouTube channels have highlighted the bug and the bug can cause iMessage clients to crash on iOS. The bug involves the black dot and pointing left emojis.
In general, whenever a Unicode bug occurs it can be resolved by deleting the conversation that contains the problematic message. These bugs are not limited to iOS alone and can affect messaging apps like WhatsApp on Android too.
It may also be possible to deal with the Unicode bug by for iOS 11.4 or macOS 10.13.5 betas via Messages on iCloud. For future instances of Unicode bugs, the same steps can be used to stop your iMessage client from crashing on your iOS or macOS device.