If a special PUSH notification comes to your phone, it will force the device to reboot or even freeze, and so that only a flashing will help. The killer's message consists of several symbols in Sindhi (the language of India and Pakistan), as well as an emoji depicting the flag of Italy. In 2015, there was already a similar bug that "hung" iPhones. But, unlike him, the new defect does not work when it appears in chats or the browser.
The beta version of the new IOS 13.4.5 has already solved the problem, but since there hasn't been an official release yet, Apple advises to turn off push notifications for a while so that your iPhone remains safe. After all, ill-wishers can use the bug for their own purposes. To do this, go to the settings, select the "Notifications" item and disable access to notifications in potentially dangerous applications - messengers and social networks.