diff --git a/mediahive/__main__.py b/mediahive/__main__.py
index 4006f32..fed0f37 100644
--- a/mediahive/__main__.py
+++ b/mediahive/__main__.py
@@ -67,7 +67,7 @@ def main() -> None:
 
     if use_gui:
         try:
-            from mediahive.winmain import winmain
+            from mediahive.winmain import gui_main
         except ImportError as exc:
             if args.gui:
                 raise RuntimeError(
@@ -75,7 +75,7 @@ def main() -> None:
                     "Install with: uv pip install mediahive[gui]"
                 ) from exc
         else:
-            winmain()
+            gui_main()
             return
 
     if args.media_folders:
diff --git a/mediahive/hivescan/scanner.py b/mediahive/hivescan/scanner.py
index b882b66..256cf11 100644
--- a/mediahive/hivescan/scanner.py
+++ b/mediahive/hivescan/scanner.py
@@ -140,15 +140,21 @@ class RootScanner:
             if task and not task.done():
                 task.cancel()
         # Wait briefly for graceful shutdown to avoid lingering scanner tasks.
-        for task in tasks:
-            if task and not task.done():
-                with contextlib.suppress(TimeoutError, asyncio.CancelledError):
-                    await asyncio.wait_for(task, timeout=2.0)
-        # Best-effort persistence of scanner state.
+        # All tasks are awaited concurrently (a slow one must not delay the
+        # others), under a single overall timeout.
+        pending = [task for task in tasks if task and not task.done()]
+        if pending:
+            with contextlib.suppress(TimeoutError, asyncio.CancelledError):
+                await asyncio.wait_for(
+                    asyncio.gather(*pending, return_exceptions=True), timeout=2.0
+                )
+        # Best-effort persistence of scanner state, concurrently.
         with contextlib.suppress(Exception):
-            await asyncio.to_thread(self._save_scan_state)
-            await asyncio.to_thread(self._save_reel_state)
-            await asyncio.to_thread(save_probe_records)
+            await asyncio.gather(
+                asyncio.to_thread(self._save_scan_state),
+                asyncio.to_thread(self._save_reel_state),
+                asyncio.to_thread(save_probe_records),
+            )
 
     def is_scanning(self) -> bool:
         return self._scan_task is not None and not self._scan_task.done()
diff --git a/mediahive/root_registry.py b/mediahive/root_registry.py
index 10dccc8..d3a91ff 100644
--- a/mediahive/root_registry.py
+++ b/mediahive/root_registry.py
@@ -353,6 +353,10 @@ class Supervisor:
 
     async def shutdown(self) -> None:
         async with self._lock:
-            for ctx in list(self._contexts.values()):
-                await ctx.stop()
+            # Stop roots concurrently — each may wait on task cancellation and
+            # network-mount snapshot flushes, and those delays must not add up.
+            await asyncio.gather(
+                *(ctx.stop() for ctx in list(self._contexts.values())),
+                return_exceptions=True,
+            )
             self._contexts.clear()
diff --git a/mediahive/winmain.py b/mediahive/winmain.py
index b564d16..f2b80f5 100644
--- a/mediahive/winmain.py
+++ b/mediahive/winmain.py
@@ -688,6 +688,46 @@ def _start_gamepad_remote(
     return thread
 
 
+def _rotate_and_open_log(log_path: Path):
+    """Rotate mediahive.log to .log.1 and open a fresh log file.
+
+    Raises OSError when a previous MediaHive instance still holds the file
+    open (Windows forbids renaming a file that is open without delete
+    sharing) — callers treat that as "previous instance not dead yet".
+    """
+    prev = log_path.with_suffix(".log.1")
+    if log_path.exists():
+        if prev.exists():
+            prev.unlink()
+        log_path.rename(prev)
+    fd = os.open(log_path, os.O_WRONLY | os.O_CREAT | os.O_TRUNC)
+    return os.fdopen(fd, "w", encoding="utf-8", buffering=1)  # line-buffered
+
+
+def _wait_for_previous_instance(log_path: Path, timeout: float = 15.0):
+    """Show a waiting notice while a previous MediaHive instance exits.
+
+    Returns an open log file handle, or None on timeout.
+    """
+    result: list = []
+    window = webview.create_window(
+        "MediaHive", html=_WAIT_HTML, width=520, height=280, resizable=False
+    )
+
+    def poll() -> None:
+        deadline = time.monotonic() + timeout
+        while time.monotonic() < deadline:
+            try:
+                result.append(_rotate_and_open_log(log_path))
+                break
+            except OSError:
+                time.sleep(0.5)
+        window.destroy()
+
+    webview.start(func=poll, icon=_icon_path(), **_webview_start_kwargs())
+    return result[0] if result else None
+
+
 def _setup_logging() -> Path:
     """Redirect stdout/stderr and configure logging to a file in %APPDATA%/mediahive/.
 
@@ -702,19 +742,30 @@ def _setup_logging() -> Path:
     log_dir.mkdir(parents=True, exist_ok=True)
     log_path = log_dir / "mediahive.log"
 
-    # Rotate: keep previous run as .log.1
-    prev = log_path.with_suffix(".log.1")
-    if log_path.exists():
-        if prev.exists():
-            prev.unlink()
-        log_path.rename(prev)
+    try:
+        log_file = _rotate_and_open_log(log_path)
+    except OSError:
+        # A previous instance still holds the log file.  It is usually on its
+        # way out — give it a couple of seconds silently first.
+        log_file = None
+        deadline = time.monotonic() + 2.0
+        while log_file is None and time.monotonic() < deadline:
+            time.sleep(0.25)
+            with contextlib.suppress(OSError):
+                log_file = _rotate_and_open_log(log_path)
+        if log_file is None:
+            log_file = _wait_for_previous_instance(log_path)
+        if log_file is None:
+            # Never fail startup over logging: fall back to a per-process file.
+            log_path = log_dir / f"mediahive-{os.getpid()}.log"
+            with contextlib.suppress(OSError):
+                fd = os.open(log_path, os.O_WRONLY | os.O_CREAT | os.O_TRUNC)
+                log_file = os.fdopen(fd, "w", encoding="utf-8", buffering=1)
 
-    fd = os.open(log_path, os.O_WRONLY | os.O_CREAT | os.O_TRUNC)
-    log_file = os.fdopen(fd, "w", encoding="utf-8", buffering=1)  # line-buffered
-
-    # Redirect raw stdout/stderr so print() and tracebacks go to the file
-    sys.stdout = log_file
-    sys.stderr = log_file
+    if log_file is not None:
+        # Redirect raw stdout/stderr so print() and tracebacks go to the file
+        sys.stdout = log_file
+        sys.stderr = log_file
 
     # force=True removes handlers added by uvicorn/fastapi during import so that
     # basicConfig actually takes effect (without it, it's a silent no-op)
@@ -743,6 +794,54 @@ _SETUP_HTML = """<!DOCTYPE html>
   <div><h1>MediaHive</h1><p>Choose a folder that contains your media…</p></div>
 </body></html>"""
 
+# Shown when a previous instance is still shutting down.
+_WAIT_HTML = """<!DOCTYPE html>
+<html><head><meta charset="utf-8"><style>
+  * { box-sizing: border-box; margin: 0; padding: 0; }
+  body { background: #141414; color: #fff;
+         font-family: 'Segoe UI', system-ui, sans-serif;
+         display: flex; align-items: center; justify-content: center;
+         height: 100vh; text-align: center; }
+  h1 { font-size: 2rem; color: #e50914; margin-bottom: .5rem; }
+  p  { color: #aaa; }
+</style></head><body>
+  <div><h1>MediaHive</h1>
+  <p>Waiting for the previous MediaHive instance to finish exiting…</p></div>
+</body></html>"""
+
+
+def _show_fatal_error(exc: BaseException) -> None:
+    """Show an unhandled exception as a TraceRite HTML page in a webview.
+
+    Frozen --windowed builds otherwise surface crashes only as PyInstaller's
+    plain-text error dialog (or nothing at all).
+    """
+    try:
+        from tracerite.html import html_traceback
+
+        fragment = str(html_traceback(exc))
+    except Exception:  # noqa: BLE001 - error reporting must never raise
+        return
+    page = (
+        "<!DOCTYPE html><html><head><meta charset='utf-8'>"
+        "<title>MediaHive — Error</title></head>"
+        f"<body style='margin:1.5rem'>{fragment}</body></html>"
+    )
+    try:
+        webview.create_window("MediaHive — Error", html=page, width=1100, height=750)
+        webview.start(icon=_icon_path(), **_webview_start_kwargs())
+    except Exception:
+        logger.exception("Could not display the error window")
+
+
+def gui_main() -> None:
+    """Run the GUI, rendering fatal exceptions as a TraceRite HTML window."""
+    try:
+        winmain()
+    except Exception as exc:
+        logger.exception("Fatal error")
+        _show_fatal_error(exc)
+
 
 class JsApi:
     """Python methods exposed to the frontend via window.pywebview.api."""
@@ -1056,4 +1155,4 @@ def winmain() -> None:
 
 
 if __name__ == "__main__":
-    winmain()
+    gui_main()