React.lazy, Suspense and the Hidden 300 ms Delay

A React 19 tab extension was experiencing a 300 ms performance delay where widgets wouldn't appear until 380 ms after opening a tab, even though the code loaded in just 100 ms. The issue wasn't the bundle size—removing unnecessary code made no measurable difference—but rather React's Suspense mechanism, which suspends lazy components once and holds them back for 300 ms by default. Rendering a placeholder directly instead of using Suspense reduced the delay to first widget appearance by approximately 240 ms.