Symptoms
Navigating to TOP > Service > Applications > Application Instances, the page loads for 5 minutes and eventually shows the error:
Error 503
Sorry, the service is not available
Try to reload page later.
There is a vast amount of APS 2.0 application instances (>20000).
Cause
The page rendering will get optimized in scope of APS-41694.
Resolution
Increase Apache timeout to 10 minutes on the Branding node(s) per the instruction from the article:
Operations in CCP fail with Service Unavailable error