ArcGIS Pro 2.9 suddenly can't sign into portal 10.9.1

[DavidColey]

Hello - we suddenly as of today cannot sign into our just-upgraded portal 10.9.1 from Pro 2.9.  A Fiddler session indicates a favicon.ico can't load, and then we don't get the login boxes:

ArcGIS Onilne:

Anyone else seeing this?

[BillFox]

are you seeing any SSL cert / expiration issues?

[DavidColey]

our sectigo CA certs are all good across the deployment, so no problems accessing anything through the browser

[DavidColey]

the api and the pro sharing module can both still access the portal . . . 

[DavidColey]

This is odd, the option to 'sign in using browser' just came available and so I am now able to get into my portal that way.  Waiting to hear back from my IT Security to see if they changed anything. 

I did have windows updates apply during a restart yesterday afternoon (12/1421, ~ 3:00 pm EST).  They may have just rolled back that change.

[DEWright_CA]

I am having the exact same issues with my 2.9.

[DavidColey]

Well, the login dialog window from Pro 2.9 reappeared with username password form:

for reasons unknown.  But I can say it had nothing to do with the favicon.ico not loading.