Hi there.
The only thing I can think of with this is when it says "Intergrated Windows Auth Endpoint", is this talking about the AD account that the Azure AD tool creates? Is this still present in AD, did you delete or remove it ?
I would imagine that the answer to that is no, because you can log in to Office 365, I've recenty done one of these and to be honest, the SSO setup was the easiest part of it, the hard work started for me when I moved accounts and had all sorts of issues with internal email sending when the users were in co-existance with Exchange on premises and in the cloud.