Yesterday brought news of some OnePlus 5 phones rebooting when their owners attempted to dial 911. Today it seems that the issue is not limited to OnePlus. A redditor on r/Android is compiling a list of devices experiencing the same problem, with links to their respective comments and/or threads:
So far users in both the US and UK have reported the problem; there have been no reports from Canada as of yet, but apparently Best Buy recalled a large number of ASUS phones here. The source of the issue has yet to be confirmed, but it’s suspected to be something to do with the AOSP dialer; all background processes are supposed to be halted when a 911 call is initiated, but some faulty code might be interfering with this.
Installing the Google Dialer from the Play Store may or may not address the problem. Concerned users can try contacting their local police force and see if they’ll arrange a test call to their 911 service.