Blue switch momentary flicker due to network traffic?

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1

I have a Blue smart dimmer switch connected to z2m & home assistant.

This switch has a single LED bulb as the load and is configured as a dimmer.

Randomly, this bulb will flicker sharply for ~250-500ms and it’s incredibly distracting when it happens. It’s not a “slight” flicker so it catches your attention.

Recently I was able to trigger the behavior by using an IKEA symfonisk remote that I use to control my Sonos through HA. It didn’t happen every time I used the remote, but enough to correlate over “normal” random observations. Also note, using the remote does not always do this so I have no idea what changes behavior.

This got me thinking and I checked my network graph and the remote is linked to this switch.

I have a pretty large zigbee network with ~60 devices and ~40 inovelli switches acting as powered nodes.

Has anyone ever seen anything like this?

2

Just a thought - Have you tested other LED bulbs? Not just the same brand/model. I’ve had even uber expensive commercial lights come in DOA or at least messed up in one way or another.

I use the same switches with Hue and almost all of them worked OK when I first added them. There was a couple that didn’t work or respond well until I did a full reset of the bulb.

3

Yes I’ve tried multiple bulbs. Currently running a GE relax LED.

Again this isn’t a constant flicker or something that changes with dim level. Ive fought that in the past (and still do on one of my fixtures).

It’s this odd transient “burst” that is a very sharp flicker when it does happen.

4

Hey @dmk

That short 250–500ms sharp burst sounds a lot less like a typical LED phase/dimming mismatch and much more like a power dip or CPU interruption caused by Zigbee RF processing.

Since you correlated it with using the Symfonisk remote—and confirmed in your graph that the remote routes through this switch a few likely culprits are at play:

1. High Network Traffic / Packet Processing Interference

With 60 Zigbee devices and 40 Inovelli switches acting as heavy repeaters, high-burst traffic passing through that specific switch (like rapid rotary/media commands from the Symfonisk) can cause a momentary internal power draw or processing spike on the switch’s microcontroller. In some firmware revisions, heavy Zigbee TX/RX processing can briefly affect the MOSFET dimming drive circuit, causing that transient flash.

2. Unintended Direct Binding or Multicast Traffic

Since the remote is routed through or bound near the switch, check if the Symfonisk remote accidentally has a direct Zigbee binding (or is sending a multicast broadcast command) to the switch’s endpoint rather than just sending events to Home Assistant. A rogue/misinterpreted ZCL command (like a stray Move to Level or Step command) could cause a fraction of a second output jump before HA or the switch overrides it.

Recommended Next Steps to Troubleshoot:

  1. Check / Update Switch Firmware: Make sure your Blue switch is on the latest firmware (v2.15+ or latest target). Recent updates specifically optimized Zigbee message handling, reduced unnecessary broadcast processing, and fixed transient power delivery quirks during high RF traffic.

  2. Check Bindings in Z2M: Open the Symfonisk remote in Zigbee2MQTT, navigate to the Bind tab, and confirm it isn’t bound directly to the Blue switch or an active group that includes it. Unbind if necessary.

  3. Try Trailing-Edge Dimming (if applicable): If you haven’t already, try switching the dimming mode (Parameter 22 / Phase Control) between leading-edge and trailing-edge in Z2M to see if the bulb’s power circuit tolerates transient RF bursts better in one mode over the other.

  4. Isolate the Mesh Route: As a quick test, force the Symfonisk remote to re-pair closer to another router (or re-route) so its heavy burst traffic stops hopping through that specific light switch.

Do you know what firmware version you’re currently running on that switch!