A particular string of characters in the Sindhi language seems to be wreaking havoc on iOS devices worldwide. Upon receiving the text in question, iOS crashes completely. A force restart is required to get the iPhone/iPad operational again. The only workaround is to disable notifications for all instant messaging applications until Apple rolls out a fix.
https://www.notebookcheck.net/A-string-of-text-with-Sindhi-characters-is-crashing-iOS-devices-worldwide.462514.0.html