That a disease can be very contagious and risk life to die.
People were eager to return to Philadelphia and get back to their normal lives. George Washington was especially interested in returning to Philadelphia so Congress could meet and keep the government running. However, people often returned too soon, and the yellow fever was not yet gone. It was still lingering in people's homes, which caused people to continue getting sick.
the Isle of Dogs is generally a play written by Thomas Na-she and Ben Johnson. this play was performed in 1597 in London, it was considered slanderous and offensive even that the writer was arrested and no single copy of it was ever found.
The privy council orders the closure not just the play but that theater where it was performed in London, it takes further to closure of all theaters in London.