diff --git a/monitor.py b/monitor.py
index 9effb14..8f97934 100644
--- a/monitor.py
+++ b/monitor.py
@@ -694,6 +694,8 @@ class NetworkMonitor:
         hosts_with_regression: List[str] = []
 
         for instance, ifaces in states.items():
+            if instance not in self._instance_map:
+                continue  # skip unconfigured Prometheus instances
             host = self._hostname(instance)
             new_baseline.setdefault(host, {})
             host_has_regression = False
@@ -877,6 +879,8 @@ class NetworkMonitor:
 
         hosts = {}
         for instance, ifaces in iface_states.items():
+            if instance not in self._instance_map:
+                continue  # skip Prometheus instances not in config (e.g. LXC app servers)
             host = self._hostname(instance)
             phys = {k: v for k, v in ifaces.items()}
             up_count = sum(1 for v in phys.values() if v)