Warning about potential memory leak when placeholder is true

[feg624]

When "placeholder" attribute is true, and after having scrolled forward (the placeholder image was rendered), and then scrolling back to the beginning of the list, the following warning is shown on the web version:

Warning: Can't perform a React state update on an unmounted component. This is a no-op, but it indicates a memory leak in your application. To fix, cancel all subscriptions and asynchronous tasks in a useEffect cleanup function. at http://localhost:19006/static/js/bundle.js:127712:34 at div at http://localhost:19006/static/js/bundle.js:134488:25 at AnimatedComponent (http://localhost:19006/static/js/bundle.js:141995:37) at AnimatedComponentWrapper at BigListPlaceholder (http://localhost:19006/static/js/bundle.js:74833:24)