Unable to start cloudShell

I myself have seen this issue and my issue was resolved by logging support case. I'd advise to log support case under Service: Account and Category: Other account issues.

AWS Support is well equipped to help you out in such scenarios, there is nothing you can do here.

I've seen users in re:Post community as well, who have faced similar issue and got it resolved by contacting AWS Support.

Please refer this thread.

Hope you find this useful.

Comment here if you have additional questions.

Abhishek