diff --git a/backend/src/module/downloader/client/aria2_downloader.py b/backend/src/module/downloader/client/aria2_downloader.py
index dfa78a5f..d68e52b8 100644
--- a/backend/src/module/downloader/client/aria2_downloader.py
+++ b/backend/src/module/downloader/client/aria2_downloader.py
@@ -49,6 +49,10 @@ class Aria2Downloader:
                 )
                 await asyncio.sleep(5)
                 times += 1
+        # Failed auth: close the client here or its connection pool leaks,
+        # because DownloadClient.__aenter__ raises before __aexit__ can run.
+        await self._client.aclose()
+        self._client = None
         return False
 
     async def logout(self):
diff --git a/backend/src/module/downloader/client/qb_downloader.py b/backend/src/module/downloader/client/qb_downloader.py
index fc08bde7..bbf229dc 100644
--- a/backend/src/module/downloader/client/qb_downloader.py
+++ b/backend/src/module/downloader/client/qb_downloader.py
@@ -47,7 +47,9 @@ class QbDownloader:
                     self._url("auth/login"),
                     data={"username": self.username, "password": self.password},
                 )
-                if resp.status_code == 200 and resp.text == "Ok.":
+                # qBittorrent < 5.2 answers 200 + "Ok." / "Fails.";
+                # qBittorrent >= 5.2 answers 204 with an empty body on success (#1044).
+                if resp.status_code in (200, 204) and "fails" not in resp.text.lower():
                     return True
                 elif resp.status_code == 403:
                     logger.error("Login refused by qBittorrent Server")
@@ -80,6 +82,10 @@ class QbDownloader:
                 else:
                     logger.error(f"Unknown error: {e}")
                 break
+        # Failed auth: DownloadClient.__aenter__ raises before __aexit__ can run,
+        # so the client must be closed here or its connection pool leaks.
+        await self._client.aclose()
+        self._client = None
         return False
 
     async def logout(self):
@@ -201,11 +207,22 @@ class QbDownloader:
         resp = await self._client.get(self._url("torrents/info"), params={"tag": tag})
         return resp.json()
 
-    async def torrents_delete(self, hash, delete_files: bool = True):
-        await self._client.post(
+    async def torrents_delete(self, hash, delete_files: bool = True) -> bool:
+        # qBittorrent expects one pipe-joined "hashes" field; a Python list would
+        # be form-encoded as repeated fields and silently ignored (#1046).
+        hashes = "|".join(hash) if isinstance(hash, (list, tuple)) else hash
+        resp = await self._client.post(
             self._url("torrents/delete"),
-            data={"hashes": hash, "deleteFiles": str(delete_files).lower()},
+            data={"hashes": hashes, "deleteFiles": str(delete_files).lower()},
         )
+        if resp.status_code != 200:
+            logger.error(
+                "[Downloader] Failed to delete torrents %s: HTTP %s",
+                hashes,
+                resp.status_code,
+            )
+            return False
+        return True
 
     async def torrents_pause(self, hashes: str):
         await self._client.post(
diff --git a/backend/src/test/test_qb_downloader.py b/backend/src/test/test_qb_downloader.py
index f90a370c..81ee209f 100644
--- a/backend/src/test/test_qb_downloader.py
+++ b/backend/src/test/test_qb_downloader.py
@@ -528,3 +528,116 @@ class TestUrlHelper:
             host="http://nas.local:8080", username="u", password="p", ssl=True
         )
         assert qb._url("torrents/info") == "http://nas.local:8080/api/v2/torrents/info"
+
+
+# ---------------------------------------------------------------------------
+# qBittorrent 5.2 login compatibility (#1044, #1034, #1043)
+# ---------------------------------------------------------------------------
+
+
+class TestAuthQb52Compat:
+    """qBittorrent >= 5.2 returns HTTP 204 with an empty body on success."""
+
+    async def test_auth_returns_true_on_204_empty_body(self):
+        """Returns True when server responds 204 + empty body (qB >= 5.2)."""
+        qb = QbDownloader(
+            host="localhost:8080", username="admin", password="pass", ssl=False
+        )
+
+        mock_client = AsyncMock()
+        mock_resp = MagicMock()
+        mock_resp.status_code = 204
+        mock_resp.text = ""
+        mock_client.post = AsyncMock(return_value=mock_resp)
+
+        with patch(
+            "module.downloader.client.qb_downloader.httpx.AsyncClient",
+            return_value=mock_client,
+        ):
+            result = await qb.auth()
+
+        assert result is True
+
+    async def test_auth_returns_false_on_200_fails_body(self):
+        """Returns False on 200 + 'Fails.' (bad credentials, qB < 5.2)."""
+        qb = QbDownloader(
+            host="localhost:8080", username="admin", password="wrong", ssl=False
+        )
+
+        mock_client = AsyncMock()
+        mock_resp = MagicMock()
+        mock_resp.status_code = 200
+        mock_resp.text = "Fails."
+        mock_client.post = AsyncMock(return_value=mock_resp)
+
+        with (
+            patch(
+                "module.downloader.client.qb_downloader.httpx.AsyncClient",
+                return_value=mock_client,
+            ),
+            patch(
+                "module.downloader.client.qb_downloader.asyncio.sleep",
+                new_callable=AsyncMock,
+            ),
+        ):
+            result = await qb.auth(retry=1)
+
+        assert result is False
+
+    async def test_auth_closes_client_on_failure(self):
+        """A failed auth must aclose() the httpx client (leak fix)."""
+        qb = QbDownloader(
+            host="localhost:8080", username="admin", password="pass", ssl=False
+        )
+
+        mock_client = AsyncMock()
+        mock_resp = MagicMock()
+        mock_resp.status_code = 403
+        mock_resp.text = "Forbidden"
+        mock_client.post = AsyncMock(return_value=mock_resp)
+
+        with patch(
+            "module.downloader.client.qb_downloader.httpx.AsyncClient",
+            return_value=mock_client,
+        ):
+            result = await qb.auth()
+
+        assert result is False
+        mock_client.aclose.assert_awaited_once()
+        assert qb._client is None
+
+
+# ---------------------------------------------------------------------------
+# torrents_delete (#1046)
+# ---------------------------------------------------------------------------
+
+
+class TestTorrentsDelete:
+    """torrents_delete must pipe-join hash lists and report failures."""
+
+    async def test_delete_joins_hash_list_with_pipe(self):
+        """A list of hashes is sent as a single pipe-joined string."""
+        qb = QbDownloader(host="localhost:8080", username="u", password="p", ssl=False)
+        qb._client = AsyncMock()
+        mock_resp = MagicMock()
+        mock_resp.status_code = 200
+        qb._client.post = AsyncMock(return_value=mock_resp)
+
+        result = await qb.torrents_delete(["aaa", "bbb"], delete_files=True)
+
+        assert result is True
+        sent = qb._client.post.call_args.kwargs["data"]
+        assert sent["hashes"] == "aaa|bbb"
+        assert sent["deleteFiles"] == "true"
+
+    async def test_delete_returns_false_on_error_status(self):
+        """Non-200 response returns False instead of silently succeeding."""
+        qb = QbDownloader(host="localhost:8080", username="u", password="p", ssl=False)
+        qb._client = AsyncMock()
+        mock_resp = MagicMock()
+        mock_resp.status_code = 403
+        qb._client.post = AsyncMock(return_value=mock_resp)
+
+        result = await qb.torrents_delete("aaa", delete_files=True)
+
+        assert result is False