Hi,
I have my Forerunner 265 for a 1/2 year after owning a 235 for few years.
the 265 from the beginning had issues with heart rate monitoring.
I'm using it mainly in my mountain biking and in a lot of times does not "lock" on my heart rate and I need to move it and shake it a lot for it to lock and show the correct values. and I need to do it several times in each ride.
I did everything that was suggested in any thread over the internet. upgrade to the "fixed" FW version, did all the tips that should help. nothing helped.
I must say that my 235 never had such issues and when I wear both of them I can see the different.
I'm a FW developer engineer, I can't understand how you have a working feature on one platform (235) and when moving to a new platform (265) it breaks and you still release the product to customers.
a shame.
For sure my next watch will not be a Garmin. there are good competitors.