Quick answer: Godot 4 pooled instance's tween method call running on the previous instance's data? Pool reuses; tween state from previous use persists - kill all tweens on pool acquire.
Pickup item from pool; tween scale from 0 to 1; tween triggered from a previous use's leftover.
Kill tweens on acquire
get_tree().get_tweens() filtered for the node; kill each. Fresh state.
Or use a per-pool acquire callback
Each acquire triggers a cleanup. Centralized.
Audit pool reuse
Each pooled object: what state must be cleaned. The cleanup checklist is the contract.
“Pool acquire skips construction. Construction-time cleanups skip too.”
Build a per-pool 'acquire' helper. The cleanup is explicit; bugs avoid.