We use ADFS 3.0 with AADSync to log in to the O365 services but our users are sometimes unable to logon.
Once in a while a user get stuck on the (ADFS) logon page. When submitting the correct username and password, the login page just reloads (without any error message). The user is unable to get passed the logon page.
Clearing the cookies usually solves the issue, but not all users know how to do this and it can be hard to perform on a mobile.
We suspect the issue is related to a cookie gettig corrupt, it seems that for our ADFS environment there are 2 cookies MSISAuth (same name, same path, same domain) of which one is not a base64 encoded string (the one that starts with AAEAA)?!