New beta is out 19.09

So then we know why the LEDs stay on when we run with a chest strap.

But the open question remain - what Garmin mean under "the best heart rate data source" - showing "more"

 or "less" or?..

OHRS should always be on second place, simple always. It is better have no HR than "some" HR from OHRS on activity to me.

I agree. Whenever there is a signal from the chest strap, that should be the best source.

In some rare cases it happened to me that my chest strap had "gone crazy" and it showed super high HR values while I was at a moderate effort, probably because it wasn't wet enough. That may be one case when the OHR might be a temporarily better source.

How about another example - i do interval exercise - accelerate from pace 6.00 to 3.30 for a 60 sec - the strap  shows "crazy high" HR and OHR lost a plot and shows "somewhat" in between. What happens now? 

Yes that's true, but I expect them to have added some algorithm that is capable of understanding if the exceptional high reading is caused by a problem or by your real effort.

That said, it is true that, in the event that this didn't work correctly, it could be a good idea to insert a switch in the settings to choose to enable or disable this.

I haven't used the beta or a chest strap and have a suggestion, but excuse my ignorance if I'm wrong.

Some people are unhappy that the OHR stays on while using a chest strap and it's been suggested that it might be because of security for Garmin Pay. If that's the case it would be easy to keep it off (to save battery) and just ask for the PIN again when you want to use the wallet.

The reason they have to keep the HR sensor on all the time is to check if your watch was ever removed from your wrist between two Garmin Pay uses. Checking if you have a pulse just while you are using the Garmin Pay app just indicates whether or not a person is wearing the watch, but it doesn't give any information on who is using it. So a thief would just have to put the watch on his wrist to use Garmin Pay without a pin (not secure at all).

That said, we now know that there is another reason why Garmin decided to leave the HR sensor on, and that is to provide a fallback HR source in the event that the HR strip fails.

The latest beta fw version has just added the possibility to choose whether to leave the OHR always on or not, so this seems not to be a problem anymore.

Makes sense and I realized my idea was flawed. I'm guessing it will just work as normal where they ask for the PIN again.