We have a custom list app and under SP2016 all the people picker fields are not working...
Most people are getting a 'JSON" is undefined
Click the OK and then you can put in a name in the dialog box but it just spins
1)In the IE, click on the Settings icon then click on "Compatibility View Settings". In the Compatibility View Settings page uncheck "Display intranet sites in Compatibility View" as shown in the fig below:
Now close your browser and try again. It should resolve the issue.
Then close the browser and try again. it should solve the issue.