Issue with my Verity Sense during swimming

I just got the Verity Sense and was excited to use it during my swimming session today. Unfortunately it didn't work.

I used it on my bicep, pushed the button to turn it on and, just like the manual tells you, pushed the button again after the light hit the swimming symbol. All lights started to light up which should mean that the sensor started to record the swimming session.

I stopped the recording after the session, synced the sensor with my phone but nothing was recorded.

What did I do wrong? Hope that someone here has some advice :)