diff --git a/server.ts b/server.ts
index 571659a..95102a2 100644
--- a/server.ts
+++ b/server.ts
@@ -757,6 +757,13 @@ async function startServer() {
         const state: number | undefined = host?.extensions?.state;
         if (name !== undefined && state !== undefined) hostnameToState.set(name, state);
       }
+
+      // Diagnostic: log a sample so mismatches between config and monitoring IDs are visible
+      const cfgSample = [...ipToHostname.values()].slice(0, 3).join(', ');
+      const monSample = [...hostnameToState.keys()].slice(0, 3).join(', ');
+      db.prepare('INSERT INTO logs (id, timestamp, type, message) VALUES (?, ?, ?, ?)')
+        .run(uid('log'), now, 'system',
+          `CheckMK diagnostic — config hosts (${ipToHostname.size}): [${cfgSample}] | monitoring hosts (${hostnameToState.size}): [${monSample}]`);
     } catch (err: any) {
       const msg = `CheckMK sync failed — could not fetch monitoring states: ${err?.message ?? err}`;
       console.error('[CheckMK]', msg);