The "Tibco Nimbus has encountered a redirect loop" error may occur due to below possible reasons,

1) When we use the web client URL of the process map on the landing page.
2) When the "Server.npdta" file has the wrong URL.
3) When URL requires "HTTPS://" protocol to run but the landing page has "HTTP://" protocol

You can resolve the "Tibco Nimbus has encountered a redirect loop" loop error as follows,
1) When we copy the web client URL of the process map on the landing page.
--> Open the Author Client.
--> Open the Process Map.
--> Go to Map --> "Where Am I?.."
--> Copy the URL and use it on Landing Page.

2) When the "Server.npdta" file has the wrong URL.

--> Open TIBCO Nimbus\Process Repository\ServerURL.npdta file.
--> Check if Tibco Nimbus URL is correct or not and update it.
--> Restart the webserver
--> Follow the steps mentioned in 1) cause which is to copy URL from Map --> "Where Am I?.."

3)  When URL requires "HTTPS://" protocol to run but the landing page has "HTTP://" protocol
--> Sometimes landing page URL has "HTTP://" protocol and it requires "HTTPS://" protocol
--> After adding an appropriate protocol, the Landing page should work correctly.