Before the update my staff were all 5 stars at level 20 but after the update they dropped to 4.5 stars despite the account remaining at level 20. Why is this?
You say your staff are all L20 but when I check the account you posted with the CD and TD are only L19 so it is not a surprise that they display as 4.5 stars to a L20 account.
Your Doctor is L20, can you confirm that the Doctor also displays as 4.5 star?
I have reported this to the Devs. I guess it is some sort of rounding issue as a result of the rescale but this is only speculation as I don't know the calculation behind the star rating.