A software bug prevents Moto G5 Plus owners from dialing 911 while using Verizon's VoLTE service. Lenovo has issued a temporary fix for the problem, as well as reassurance that it is working on a permanent solution.
http://www.notebookcheck.net/Verizon-s-VoLTE-service-prevents-Moto-G5-Plus-users-from-making-emergency-calls.213530.0.html