E0306: Malformed <ui.Island>

<ui.Island> wraps one island component to give it a fallback shown until it hydrates. It holds <ui.Template fallback> and the component, nothing else, can't nest, and <ui.Template> is valid only directly inside it.

Wrong

<ui.Island>
	<p>Loading…</p>
	<Chart series={p.sales} />
</ui.Island>

Right

<ui.Island>
	<ui.Template fallback><p>Loading…</p></ui.Template>
	<Chart series={p.sales} />
</ui.Island>