must not have any insulation above.

Install some if absent. A comfortable shop will be more useful.

Must I retape?

Seems necessary to me. I'd use fiberglass tape and a setting type joint
compound since the earler joint failure might have been related to a high
humidity situation.

Does taping have a purpose in addressing expansion, inferring that I should
try to retape it?

It will help prevent the surface cracks that develop in unreinforced joint
compound. Do some reading in any DIY text for more insights on the mysteries of
drywall. This NG has dozens of experts, some of whom have applied hundreds of
acres of drywall so you likely get some better posts than this one Good luck.

Joe.