Delay Motion Sensor --> lights-on - How to diagnose

Other Devices & Integrations Door Locks & Sensors
1

I have a 3-in-1 sensor that I use a lot to detect presence in a room and switch on the lights as a result. However, sometimes (say a couple of times a day) the following happens:

  1. The motion led is blinking, but nothing happens.
  2. The motion led is blinking, and lights switch on after X seconds where X could be anything from 1 to 20 seconds.

I have a Vera 3 which I bought to have an abundance of computing power so the delay has to be minimum. Network heals on a regular basis.

My question:

  1. When a 10 second delay strikes: What can be the reason? Is the motion message to Vera delayed? Is the switch-on message delayed? Is Vera doing other things than receiving and sending Z-Wave messages?
  2. If Vera is busy, WHAT is it doing?
  3. Not sure if timings in the /var/msg LuaUPnP logging are correct since the logging may also be off.