UniFi reports STP state flapping and the uplink keeps dropping. Is there a network loop?

Applies to: UniFi switches and bridged access points reporting repeated STP/RSTP topology changes.

Work through these checks

1. Capture the affected ports, event times and a simple connection diagram. Compare physical link-up/down events with STP changes; identify whether one cable or switch consistently changes first.
2. Check for unintended second paths, including a wired AP that also meshes, bridged end devices or a second cable between switches without a configured aggregation design. Trace the real wiring before disconnecting anything.
3. During agreed downtime, test the suspect path with a known-good cable and compatible port. A temporary lower-speed test can help isolate negotiation problems but is not proof that a persistent hardware fault is solved.
4. Ask the network administrator to review root-switch priorities, redundant paths and appropriate edge-port protections. Use STP Edge or BPDU Guard only on ports whose role is understood.

Confirm the result

The intended topology converges and stays stable through the normal workload, without repeated link or STP change events.

If you need help

Include these details in your ticket: Models, firmware, port/event screenshots, cabling diagram and results from one controlled path test.

Updated 261107