Around two days ago multiple reports started coming out saying that some OnePlus 5 units instantly rebooted when you tried to dial 911. That's obviously a huge issue, and the fact that many people seemed to encounter it only made things worse for the Chinese company. Yesterday OnePlus reached out with an official statement, saying it has tested a software update that resolved the issue, and that this would roll out to all devices in a short while. Well, that's what's happening now. As you can see from the screenshot, if you own a OnePlus 5 you'll soon be offered an update to OxygenOS...
Source: http://www.gsmarena.com/oneplus_5_update_rolling_out_with_fix_for_rebooting_when_calling_911-news-26312.php