Heart rate discrepency

[JonWFergus]

Just finished a run. If I view my heart rate in the exercise section of the app, it says I reached a max of 209bpm! But if I go into the heart rate section of the app, it shows my max at 156bpm. These two displays are for the exact same peak moment. For the intensity I ran I would expect my bpm to max out at around 180 or so. 209 seems high, 156 seems low.

So... why the discrepency? How can I trust these numbers? 156 vs 209 is a massive difference. 

[JonWFergus]

Here's the example I mentioned, plus a second one. 

 

 

So what is it, 209 or 156?

And a second time:

 

 

200 or 159?

Can anyone tell me why there is such a huge discrepancy here? 

[JonWFergus]

Just gonna continue documenting this. Here's from a 10k run today.

 

 

 

What I'm also wondering is if this is affecting my VO2Max level, which is showing at 60 (highest it's been is 63). I'm definitely not a peak athlete, so that seems high. But could it be high because fitbit is reading a mistaken heart rate when making its calculations?