When creating a Tween using TweenService, the instance is collected unless it has an active Lua reference. This causes code that aims to reference (and maybe later parent) the instance via Tween.Instance to fail because it is nil. Likewise, code that relies on Tween.Completed to fire will not work as it never fires despite calling the tween to start.
The bug happens in game, and I’m not sure how long it’s been happening. I’ve provided a single script repro below.
bad_tween.rbxl (21.2 KB)