Thank you for using Apple Support Communities!
I understand from your post that you see double carrots to the right of Invitees when creating a calendar event. In a situation like this quitting the app and restarting your iPhone is a good place to start. The following articles will provide you with the steps:
How to force an app to close on your iPhone, iPad, or iPod touch - Apple Support
Restart your iPhone, iPad, or iPod touch - Apple Support
If the issue persists, let us know so we can further assist you.
Best Regards.