diff --git a/backend/routers/issues.py b/backend/routers/issues.py
index 2ad27ca3..a20c9fbf 100644
--- a/backend/routers/issues.py
+++ b/backend/routers/issues.py
@@ -9,8 +9,10 @@
 import os
 import logging
 import hashlib
+import json
 from datetime import datetime, timezone
 
+from fastapi import Response
 from backend.database import get_db
 from backend.models import Issue, PushSubscription
 from backend.schemas import (
@@ -297,10 +299,11 @@ def get_nearby_issues(
     """
     try:
         # Check cache first
-        cache_key = f"{latitude:.5f}_{longitude:.5f}_{radius}_{limit}"
-        cached_data = nearby_issues_cache.get(cache_key)
-        if cached_data:
-            return cached_data
+        # v2: cache JSON string to avoid conflicts with v1 list data and ensure safe typing
+        cache_key = f"v2_nearby_{latitude:.5f}_{longitude:.5f}_{radius}_{limit}"
+        cached_json = nearby_issues_cache.get(cache_key)
+        if cached_json:
+            return Response(content=cached_json, media_type="application/json")
 
         # Query open issues with coordinates
         # Optimization: Use bounding box to filter candidates in SQL
@@ -345,9 +348,12 @@ def get_nearby_issues(
         ]
 
         # Update cache
-        nearby_issues_cache.set(nearby_responses, cache_key)
+        # Optimize: Cache serialized JSON string to avoid serialization overhead on subsequent requests
+        data_dicts = [m.model_dump(mode='json') for m in nearby_responses]
+        json_content = json.dumps(data_dicts, default=str)
+        nearby_issues_cache.set(json_content, cache_key)
 
-        return nearby_responses
+        return Response(content=json_content, media_type="application/json")
 
     except Exception as e:
         logger.error(f"Error getting nearby issues: {e}", exc_info=True)
@@ -659,10 +665,11 @@ def get_recent_issues(
     offset: int = Query(0, ge=0, description="Number of issues to skip"),
     db: Session = Depends(get_db)
 ):
-    cache_key = f"recent_issues_{limit}_{offset}"
-    cached_data = recent_issues_cache.get(cache_key)
-    if cached_data:
-        return JSONResponse(content=cached_data)
+    # v2: cache JSON string to avoid conflicts with v1 list data and ensure safe typing
+    cache_key = f"v2_recent_issues_{limit}_{offset}"
+    cached_json = recent_issues_cache.get(cache_key)
+    if cached_json:
+        return Response(content=cached_json, media_type="application/json")
 
     # Fetch issues with pagination
     # Optimized: Use column projection to fetch only needed fields
@@ -700,5 +707,7 @@ def get_recent_issues(
         })
 
     # Thread-safe cache update
-    recent_issues_cache.set(data, cache_key)
-    return data
+    # Optimize: Cache serialized JSON string to avoid serialization overhead on subsequent requests
+    json_content = json.dumps(data, default=str)
+    recent_issues_cache.set(json_content, cache_key)
+    return Response(content=json_content, media_type="application/json")
diff --git a/backend/tests/test_issues_cache_mocked.py b/backend/tests/test_issues_cache_mocked.py
new file mode 100644
index 00000000..7245c2aa
--- /dev/null
+++ b/backend/tests/test_issues_cache_mocked.py
@@ -0,0 +1,144 @@
+import pytest
+import json
+import sys
+import os
+from datetime import datetime, timezone
+from unittest.mock import MagicMock, patch
+
+# Mock heavy/missing dependencies before importing app
+sys.modules['magic'] = MagicMock()
+sys.modules['telegram'] = MagicMock()
+sys.modules['telegram.ext'] = MagicMock()
+sys.modules['google'] = MagicMock()
+sys.modules['google.generativeai'] = MagicMock()
+sys.modules['google.cloud'] = MagicMock()
+sys.modules['firebase_admin'] = MagicMock()
+sys.modules['firebase_functions'] = MagicMock()
+sys.modules['speech_recognition'] = MagicMock()
+sys.modules['transformers'] = MagicMock()
+sys.modules['ultralytics'] = MagicMock()
+sys.modules['cv2'] = MagicMock()
+sys.modules['pywebpush'] = MagicMock()
+sys.modules['langdetect'] = MagicMock()
+sys.modules['googletrans'] = MagicMock()
+sys.modules['a2wsgi'] = MagicMock()
+
+# Mock torch properly for scipy/sklearn checks
+mock_torch = MagicMock()
+class MockTensor: pass
+mock_torch.Tensor = MockTensor
+sys.modules['torch'] = mock_torch
+
+# Now import app
+from fastapi.testclient import TestClient
+from backend.main import app
+from backend.database import get_db
+
+client = TestClient(app)
+
+@pytest.fixture
+def mock_db_session():
+    mock_session = MagicMock()
+    app.dependency_overrides[get_db] = lambda: mock_session
+    yield mock_session
+    app.dependency_overrides = {}
+
+@pytest.fixture
+def mock_caches():
+    with patch("backend.routers.issues.recent_issues_cache") as mock_recent, \
+         patch("backend.routers.issues.nearby_issues_cache") as mock_nearby:
+
+        # Default behavior: cache miss
+        mock_recent.get.return_value = None
+        mock_nearby.get.return_value = None
+
+        yield mock_recent, mock_nearby
+
+def test_get_recent_issues_cache_miss_then_hit(mock_db_session, mock_caches):
+    mock_recent, _ = mock_caches
+
+    # Setup DB return
+    mock_issue = MagicMock()
+    mock_issue.id = 1
+    mock_issue.category = "Road"
+    mock_issue.description = "Test Issue"
+    mock_issue.created_at = datetime.now(timezone.utc)
+    mock_issue.image_path = None
+    mock_issue.status = "open"
+    mock_issue.upvotes = 0
+    mock_issue.location = "Test Loc"
+    mock_issue.latitude = 10.0
+    mock_issue.longitude = 20.0
+
+    # Mock the query chain
+    mock_query = mock_db_session.query.return_value
+    mock_query.order_by.return_value.offset.return_value.limit.return_value.all.return_value = [mock_issue]
+
+    # 1. Cache Miss
+    response = client.get("/api/issues/recent")
+    assert response.status_code == 200
+    data1 = response.json()
+    assert len(data1) == 1
+    assert data1[0]["id"] == 1
+
+    # Verify cache set was called
+    assert mock_recent.set.called
+    args, _ = mock_recent.set.call_args
+    cached_content = args[0]
+
+    # 2. Cache Hit
+    mock_recent.get.return_value = cached_content
+    mock_db_session.query.reset_mock()
+
+    response = client.get("/api/issues/recent")
+    assert response.status_code == 200
+    data2 = response.json()
+
+    assert data1 == data2
+    mock_db_session.query.assert_not_called()
+
+def test_get_nearby_issues_cache_miss_then_hit(mock_db_session, mock_caches):
+    _, mock_nearby = mock_caches
+
+    # Setup DB return for nearby
+    mock_issue = MagicMock()
+    mock_issue.id = 2
+    mock_issue.category = "Water"
+    mock_issue.description = "Nearby Issue"
+    mock_issue.created_at = datetime.now(timezone.utc)
+    mock_issue.status = "open"
+    mock_issue.latitude = 10.0
+    mock_issue.longitude = 20.0
+    mock_issue.upvotes = 5
+
+    # db.query(...).filter(...).all()
+    mock_query = mock_db_session.query.return_value
+    mock_query.filter.return_value.all.return_value = [mock_issue]
+
+    with patch("backend.routers.issues.find_nearby_issues") as mock_find:
+        mock_find.return_value = [(mock_issue, 15.0)] # Issue, distance
+
+        # 1. Cache Miss
+        response = client.get("/api/issues/nearby?latitude=10.0&longitude=20.0")
+        assert response.status_code == 200
+        data1 = response.json()
+        assert len(data1) == 1
+        assert data1[0]["distance_meters"] == 15.0
+
+        # Verify cache set
+        assert mock_nearby.set.called
+        args, _ = mock_nearby.set.call_args
+        cached_content = args[0]
+
+        # 2. Cache Hit
+        mock_nearby.get.return_value = cached_content
+        mock_db_session.query.reset_mock()
+        mock_find.reset_mock()
+
+        response = client.get("/api/issues/nearby?latitude=10.0&longitude=20.0")
+        assert response.status_code == 200
+        data2 = response.json()
+
+        assert data1 == data2
+        mock_db_session.query.assert_not_called()
+        mock_find.assert_not_called()