Hi @Stefanie34790806mwj3 ,
Welcome to the Premiere Pro forums! We are glad to see you here.
We've been seeing an uptick in issues related to 2nd monitors. Are you on a Windows machine? Did you update to the latest Windows build last week? We need a few more details to help with this issue. Please see: How do I write a bug report?
I hope we can help you soon. Sorry for the frustration!