Use keyed each loops to avoid errors

src/routes/posts/[[page=integer]]/+page.svelte

@@ -28,7 +28,7 @@
 </svelte:head>
 
 <ol class="years">
-	{#each groupPosts(data.posts).entries() as [year, posts]}
+	{#each groupPosts(data.posts).entries() as [year, posts] (year)}
 		<li>
 			<h2>{year}</h2>
 			<BlogPostList {posts} />

src/routes/posts/[[page=integer]]/BlogPostList.svelte

@@ -9,7 +9,7 @@
 </script>
 
 <ol class="posts">
-	{#each posts as post}
+	{#each posts as post (post.meta.slug)}
 		<BlogPost {post} {showYear} {showReadingTime} />
 	{/each}
 </ol>