diff --git a/backend/app/services/device_discovery.py b/backend/app/services/device_discovery.py
index 24aa85c..443bf81 100644
--- a/backend/app/services/device_discovery.py
+++ b/backend/app/services/device_discovery.py
@@ -433,4 +433,13 @@ async def discover_via_ssh(
             except Exception as exc:
                 result.errors.append(f"Error upserting {found.ip}: {exc}")
 
+        # Flush after each rack so that subsequent SELECTs (for other racks
+        # that may share the same device IPs) see the just-added rows.
+        # Without this, autoflush=False means pending db.add() calls are
+        # invisible to SELECT queries, causing UniqueViolationError on flush.
+        try:
+            await db.flush()
+        except Exception as exc:
+            result.errors.append(f"Flush error after rack {rack_host}: {exc}")
+
     return result