diff --git a/explorer.py b/explorer.py
index 4b30368..00cc37a 100644
--- a/explorer.py
+++ b/explorer.py
@@ -1777,6 +1777,11 @@ def build_trajectories_tab(db_path: str, window_size: str) -> None:
     # If no party-level centroids were computed, fall back to per-MP trajectories
     # so the user still sees a plot even when the party_map is missing or empty.
     if not centroids:
+        # Fallback: plot individual MP trajectories
+        st.info(
+            "Partijcentroiden niet beschikbaar — tonen individuele MP-trajecten als fallback."
+        )
+
         # Build per-MP time series from positions_by_window
         mp_positions: Dict[str, Dict[str, Tuple[float, float]]] = {}
         for wid in windows:
@@ -1790,20 +1795,22 @@ def build_trajectories_tab(db_path: str, window_size: str) -> None:
                     continue
                 mp_positions.setdefault(mp_name, {})[wid] = (x, y)
 
+        # Filter to MPs with at least 2 windows and not all NaN
+        mp_positions = {
+            mp: pos
+            for mp, pos in mp_positions.items()
+            if len(pos) >= 2
+            and not all(np.isnan(x) and np.isnan(y) for x, y in pos.values())
+        }
+
         if not mp_positions:
-            try:
-                _last_trajectories_diagnostics.update(
-                    {
-                        "stage": "no_mp_positions",
-                        "mp_positions_count": len(mp_positions),
-                    }
-                )
-            except Exception:
-                pass
-            try:
-                st.info("Geen positiedata beschikbaar voor trajectplotten.")
-            except Exception:
-                pass
+            st.warning("Geen positiedata beschikbaar voor trajectplotten.")
+            _last_trajectories_diagnostics.update(
+                {
+                    "stage": "no_mp_positions",
+                    "mp_positions_count": 0,
+                }
+            )
             # show diagnostics when debug enabled
             try:
                 if get_debug_trajectories_enabled():
@@ -1819,6 +1826,9 @@ def build_trajectories_tab(db_path: str, window_size: str) -> None:
                 pass
             return
 
+        # Store for later use
+        st.session_state["_trajectory_mp_positions"] = mp_positions
+
         mp_list = sorted(mp_positions.keys())
         default_mps = mp_list[:6]
         selected_mps = st.multiselect(
@@ -2170,24 +2180,41 @@ def choose_trajectory_title(axis_def: dict, axis: str, threshold: float = 0.65)
                 "sample_size": len(sample_mps),
             }
     if trace_count == 0:
-        try:
-            st.info(
-                "Geen trajecten getekend: geen geselecteerde partijen met voldoende data. Controleer de partijselectie en de 'Min. Kamerleden per partij' instelling."
+        st.info("📊 **Geen trajecten getekend**")
+
+        # Show diagnostic information
+        with st.expander("🔍 Diagnostische informatie"):
+            st.write("**Data status:**")
+            st.write(
+                f"- Positie vensters: {len(positions_by_window) if positions_by_window else 0}"
             )
-        except Exception:
-            pass
-        if debug_enabled:
-            try:
-                st.text_area(
-                    "Trajectories diagnostics",
-                    json.dumps(_last_trajectories_diagnostics, default=str),
-                    height=240,
+            st.write(f"- Party mappings: {len(party_map) if party_map else 0}")
+            st.write(
+                f"- Geselecteerde partijen: {len(selected_parties) if selected_parties else 0}"
+            )
+
+            if "centroid_diagnostics" in locals():
+                st.write("**Centroid berekening:**")
+                st.write(
+                    f"- Partijen met posities: {len(centroid_diagnostics.get('parties_with_positions', []))}"
                 )
-            except Exception:
-                try:
-                    st.json(_last_trajectories_diagnostics)
-                except Exception:
-                    pass
+                st.write(
+                    f"- Partijen met alleen NaN: {len(centroid_diagnostics.get('parties_all_nan', []))}"
+                )
+
+            st.write("\n**Mogelijke oorzaken:**")
+            st.write("1. Geen SVD vectoren berekend voor de geselecteerde vensters")
+            st.write("2. MP namen in posities komen niet overeen met party_map")
+            st.write("3. Alle geselecteerde partijen hebben te weinig MPs (< 5)")
+
+            # Add a button to run diagnostics
+            if st.button("🔧 Database diagnostiek uitvoeren"):
+                with st.spinner("Bezig met diagnostiek..."):
+                    # Import and run diagnostics
+                    from scripts.diagnose_trajectories_cli import diagnose_trajectories
+
+                    results = diagnose_trajectories(db_path)
+                    st.json(results)
     else:
         # DEBUG: show trace_count and figure data size before rendering
         try: