Testflight taking some time to assign internal group for testing

I'm experience delay since last week for Testflight to assign internal group for testing.(Within an hour its automatically added). When I tried to manually add groups to the build, It's greyed out (disabled).

Anyone knows the reason for this?

Note: Usually the build is automatically available on the testflight after processing finished.

Update: Apple took exactly 30m for this.

As I mentioned in the comments, Apple took exactly 30m to finish the process. Most probably they added some cool off time.