Disable each zigbee using app, one at a time, until the delays are gone.
When that particular app has many devices, you can cut the power from each mains powered device, again one at a time.
This (possibly) disrupts your zigbee mesh, so take your time and give the mesh network some time to recover before concluding if such a powerless device is a possible suspect.
Patrick had similar issues, this was the fix:
