Charge 3 isn't registering EOV

[CX2]

I received my Charge 3 last week, I upgraded from the charge 2 purely for the oxygen monitor as there is definitely something up with my sleep and thought this would give me some more insight. But it isn’t working.

I’ve deleted and reinstalled the app and rebooted the the Charge 3 several times but I still can only see the green light and no red lights. Can anyone help me to get it working or I will be sending it back to Amazon on Thursday.

Moderator Edit: Clarified subject

[AlejandraFitbit]

Welcome to the Community, @CX2.

Thanks for troubleshooting this EOV issue. If you move frequently during sleep, the movement can interfere with the light that bounces back to the sensors on your device. 

To receive EOV data, note the following:

• Make sure your Fitbit device is snug and secure before you go to sleep. For more information, see How do I wear my Fitbit device?
• Make sure your Fitbit device is charged.
• You must sleep 3 or more hours.

Let me know the outcome. 

[NICGuy59]

Part of the reason that the Charge 3 only does Estimated Oxygen Variations at night is due to light levels, as I understand it. 

The different LEDs on the back of the device use the difference in reflected light to get a reading.  If you don't sleep in the dark, or have some light in the room, it may affect the ability of the device to read oxygen levels.

I initially didn't have any graph (first three days of wear), but a Restart got the graph to show up (only for the nights after the reset, as I assume it didn't record anything before then).  Also, the graph disappeared suddenly a few days ago.  A poster suggested doing a 'Clear User Data' process, which I tried, and I got a graph for the night after that.  Lost the three intervening nights, but I now have a graph again.