Hi @uranus829
Glad to hear that and thanks for the sharing.
While due to the forum policy, the original poster cannot accept their own reply as the answer to the question.
I have written a summary of this issue.
Please feel free to accept it as the answer to highlight the solution to help other community members.
Thanks for your understanding.
[Exchange 2019 CU 12 Cannot login to ECP after installing new SSL certificate - Summary]
Issue Symptom:
scenario: two Exchange 2019 CU 12 servers and load balancer
Once the Exchange Oauth certificate is updated, accessing the ecp url (pointed to the load balancer) would be redirected to login page, cause the login to loop.
It may take about 8 hours for it to work correctly.
Solution:
Refer to the Workaround part in this link:
Cannot log in to OWA or ECP after July 2021 SU for Exchange Server 2019, 2016, and 2013 (KB 5005341)
You can work around the issue that's described in the "Cause 2" section by setting the persistence to “source-ip” in the load balancer configuration.