When trying to associate an ArcGIS Pro account with an ArcGIS Online account, ArcGIS Pro will attempt to sign in and never open or crash. ESRI is aware of this and is working towards a permanent solution. We are also working to get ArcGIS Pro set up to use single sign-on in the hopes that it will fix the issue as well.
In the meantime, here is a solution that will work – ArcGIS Pro Logging on Issue