Is it not clear if the effect's clean up logic from a component making using of context is ran BEFORE re-rendering any other instance of the same component (on the same hierarchy level)

Runnable example: https://codesandbox.io/s/fast-sunset-8c0z2?file=/src/App.js

What is clear: It is clear a change in context will cause all consumers to re-render.

What is not clear: When using useEffect's clean up function - ( return () => { do some clean up } ) will that always be done for ALL component instance using the same context BEFORE re-rendering the other components of the same type ( ie multiple instances of MyComp )?

issue にリンクされている実行可能な CodeSandbox の例から始め、src/App.js を調べて、コンテキストの更新と useEffect のクリーンアップの挙動を再現します。複数の MyComp インスタンス間での順序を特定し、その答えと関連する注意点を React ドキュメントの適切な場所に記載します。