HomeKit Shortcut bug fixed in iOS 15.1 / tvOS 15.1 / iPadOS 15.1 / HomePod Software Update 15.1
The bug introduced in iOS (and tvOS, etc) 15, seems now to have been fixed in the 15.1 update. If you used any of the workarounds in my earlier posts, those would of course continue to work. The Home app also seems a lot little bit more stable when writing longer HomeKit shortcuts.