diff --git a/backend/tasks/media.py b/backend/tasks/media.py
index e917975e..7446c839 100644
--- a/backend/tasks/media.py
+++ b/backend/tasks/media.py
@@ -26,6 +26,8 @@ IMAGE_EXTENSIONS = {
     ".webp",
 }
 VIDEO_EXTENSIONS = {
+    ".3gp",
+    ".avi",
     ".m4v",
     ".mkv",
     ".mov",
@@ -97,19 +99,17 @@ def _render_video_thumbnail(attachment: TaskAttachment) -> bytes:
             output_path = output_file.name
 
         filter_value = "scale=640:280:force_original_aspect_ratio=increase,crop=640:280"
-        command = [
-            ffmpeg,
-            "-hide_banner",
-            "-loglevel",
-            "error",
-            "-ss",
-            "0.5",
-            "-i",
-            input_path,
+        command_prefix = [ffmpeg, "-hide_banner", "-loglevel", "error"]
+        command_suffix = [
+            "-map",
+            "0:v:0",
             "-frames:v",
             "1",
             "-vf",
             filter_value,
+            "-an",
+            "-sn",
+            "-dn",
             "-c:v",
             "libwebp",
             "-quality",
@@ -117,22 +117,33 @@ def _render_video_thumbnail(attachment: TaskAttachment) -> bytes:
             "-y",
             output_path,
         ]
-        result = subprocess.run(
-            command,
-            capture_output=True,
-            check=False,
-            timeout=30,
-        )
-        if result.returncode != 0:
-            command[5] = "0"
-            result = subprocess.run(
-                command,
-                capture_output=True,
-                check=False,
-                timeout=30,
-            )
-        if result.returncode != 0:
-            raise RuntimeError(result.stderr.decode("utf-8", errors="replace"))
+        commands = [
+            # Fast input seek works for ordinary MP4/WebM files.
+            [*command_prefix, "-ss", "0.5", "-i", input_path, *command_suffix],
+            # Accurate output seek handles fragmented MP4/MOV screen recordings
+            # whose first keyframe cannot be reached by input seeking.
+            [*command_prefix, "-i", input_path, "-ss", "0.5", *command_suffix],
+            # Some recordings start on a non-zero timeline. In that case use the
+            # first frame FFmpeg can decode instead of requiring a timestamp.
+            [*command_prefix, "-i", input_path, *command_suffix],
+        ]
+        last_error = "FFmpeg did not produce a video thumbnail."
+        for command in commands:
+            try:
+                result = subprocess.run(
+                    command,
+                    capture_output=True,
+                    check=False,
+                    timeout=30,
+                )
+            except subprocess.TimeoutExpired as error:
+                last_error = str(error)
+                continue
+            if result.returncode == 0 and Path(output_path).stat().st_size > 0:
+                break
+            last_error = result.stderr.decode("utf-8", errors="replace")
+        else:
+            raise RuntimeError(last_error)
         return Path(output_path).read_bytes()
     finally:
         if temporary_input and input_path:
diff --git a/frontend/src/components/tasks/TaskBoardNavigator.tsx b/frontend/src/components/tasks/TaskBoardNavigator.tsx
index 3cac9c8c..9ce7d7f1 100644
--- a/frontend/src/components/tasks/TaskBoardNavigator.tsx
+++ b/frontend/src/components/tasks/TaskBoardNavigator.tsx
@@ -97,13 +97,6 @@ function boardGroupPosition(
   return board.group_positions?.[String(groupId)];
 }
 
-function boardGroupSortKey(
-  board: TaskBoardSummary,
-  groupId: number,
-): string | undefined {
-  return board.group_sort_keys?.[String(groupId)];
-}
-
 function compareBoardNames(first: TaskBoardSummary, second: TaskBoardSummary): number {
   return first.name.localeCompare(second.name, "ru") || first.id - second.id;
 }
@@ -519,14 +512,18 @@ export default function TaskBoardNavigator({
         (effectiveBoardSort === "priority" || effectiveBoardSort === "priority-desc")
         && typeof effectiveGroupFilter === "number"
       ) {
-        const firstRank = boardGroupSortKey(first, effectiveGroupFilter);
-        const secondRank = boardGroupSortKey(second, effectiveGroupFilter);
-        if (firstRank && secondRank && firstRank !== secondRank) {
+        const firstPosition = boardGroupPosition(first, effectiveGroupFilter);
+        const secondPosition = boardGroupPosition(second, effectiveGroupFilter);
+        if (
+          firstPosition !== undefined
+          && secondPosition !== undefined
+          && firstPosition !== secondPosition
+        ) {
           const direction = effectiveBoardSort === "priority-desc" ? -1 : 1;
-          return (firstRank < secondRank ? -1 : 1) * direction;
+          return (firstPosition - secondPosition) * direction;
         }
-        if (firstRank && !secondRank) return -1;
-        if (!firstRank && secondRank) return 1;
+        if (firstPosition !== undefined && secondPosition === undefined) return -1;
+        if (firstPosition === undefined && secondPosition !== undefined) return 1;
       }
 
       if (effectiveBoardSort === "name-desc") {
diff --git a/frontend/src/components/tasks/TaskCommentAttachment.tsx b/frontend/src/components/tasks/TaskCommentAttachment.tsx
index e6f17fbd..76d6cdb2 100644
--- a/frontend/src/components/tasks/TaskCommentAttachment.tsx
+++ b/frontend/src/components/tasks/TaskCommentAttachment.tsx
@@ -98,7 +98,7 @@ export default function TaskCommentAttachment({
         <button
           type="button"
           onClick={() => void openPreview()}
-          disabled={!thumbnailSource || thumbnailFailed || previewLoading}
+          disabled={previewLoading}
           className="group relative block aspect-video min-h-32 w-full overflow-hidden bg-[var(--surface-secondary)] outline-none focus-visible:ring-2 focus-visible:ring-sky-400/70 disabled:cursor-default"
           title={`Просмотреть ${attachment.file_name}`}
         >
@@ -113,7 +113,15 @@ export default function TaskCommentAttachment({
             />
           ) : (
             <span className="app-text-muted absolute inset-0 flex items-center justify-center">
-              {thumbnailFailed ? <FileText size={20} /> : <Loader2 size={18} className="animate-spin" />}
+              {previewLoading ? (
+                <Loader2 size={20} className="animate-spin" />
+              ) : thumbnailFailed ? (
+                <span className="app-selected inline-flex h-11 w-11 items-center justify-center rounded-full">
+                  {video ? <Play size={20} fill="currentColor" /> : <Eye size={20} />}
+                </span>
+              ) : (
+                <Loader2 size={18} className="animate-spin" />
+              )}
             </span>
           )}
           {thumbnailSource ? (