After 8-9 months since this issue has been solved I am having the same exact issue. It started 13th of November. I am unable to connect my Apple Watch to Zwift. All apps/software are up to date.
Come on Zwift, fix it finally.
It’s never been formally fixed. The fact you’ve had it working is more luck than anything else.
An attempt at resolving the issue was made but those changes were reverted.
It still remains on the to do list.