diff --git a/app.py b/app.py
index 739e7c1..a71cbe8 100644
--- a/app.py
+++ b/app.py
@@ -371,8 +371,8 @@ def api_diagnose_start():
         return jsonify({'error': 'No link_stats data available'}), 503
     try:
         link_data = json.loads(raw)
-    except Exception:
-        logger.error('Failed to parse link_stats JSON in /api/diagnose')
+    except Exception as e:
+        logger.error(f'Failed to parse link_stats JSON in /api/diagnose: {e}')
         return jsonify({'error': 'Internal data error'}), 500
 
     switches = link_data.get('unifi_switches', {})
@@ -396,6 +396,9 @@ def api_diagnose_start():
         return jsonify({'error': 'No LLDP neighbor data for this port'}), 400
 
     server_name = lldp['system_name']
+    if not re.fullmatch(r'[a-zA-Z0-9._-]+', server_name):
+        logger.error(f'Refusing diagnostic: invalid server_name from LLDP: {server_name!r}')
+        return jsonify({'error': 'LLDP neighbor name contains invalid characters'}), 400
     lldp_port_id = lldp.get('port_id', '')
 
     # Find matching host + interface in link_stats hosts
@@ -421,9 +424,14 @@ def api_diagnose_start():
     # Resolve host IP from link_stats host data
     host_ip = (server_ifaces.get(matched_iface) or {}).get('host_ip')
     if not host_ip:
-        # Fallback: use LLDP mgmt IPs
-        mgmt_ips = lldp.get('mgmt_ips') or []
-        host_ip = mgmt_ips[0] if mgmt_ips else None
+        # Fallback: use first valid IP from LLDP mgmt IPs
+        for candidate in (lldp.get('mgmt_ips') or []):
+            try:
+                ipaddress.ip_address(candidate)
+                host_ip = candidate
+                break
+            except ValueError:
+                continue
     if not host_ip:
         return jsonify({'error': 'Cannot determine host IP for SSH'}), 400
 
diff --git a/monitor.py b/monitor.py
index 63b16a8..445912d 100644
--- a/monitor.py
+++ b/monitor.py
@@ -966,6 +966,7 @@ class NetworkMonitor:
 
             except Exception as e:
                 logger.error(f'Monitor loop error: {e}', exc_info=True)
+                time.sleep(30)
 
             time.sleep(self.poll_interval)
 
diff --git a/templates/inspector.html b/templates/inspector.html
index d33e9a6..98d0f47 100644
--- a/templates/inspector.html
+++ b/templates/inspector.html
@@ -231,6 +231,7 @@ function selectPort(el) {
 }
 
 function closePanel() {
+  if (_diagPollTimer) { clearInterval(_diagPollTimer); _diagPollTimer = null; }
   document.getElementById('inspector-panel').classList.remove('open');
   document.querySelectorAll('.switch-port-block.selected')
     .forEach(el => el.classList.remove('selected'));