Max heart rate keeps being updated

have you restarted the watch - it can often fix bug issues like this

Thank you for your answer. Just one question, would if I do that, would I lose everything? I am currently training for another marathon using the Daily Suggested Workouts which has some dates specified for each stage of the marathon plan, would I lose that too?

not a factory restore - just a reboot - turn on and off. Hold the light button until the watch turns off (first the control menu will come up, continue holding, then the live assistance option will come up - continue holding - and eventually it will turn off - release button - if it doesn't reboot within 15s then press light button to restart watch). Will not affect any settings or data.

My bad, you're right, I'll try your suggestion, thank you!

jaamgans said:

Will not affect any settings or data

Not quite true. Any unsynced 24/7 data will be lost. If you want to keep steps etc sync with phone first. 

a factory restore yes - but a hard reboot no- never lost any data with a hard reboot as you aren't clearing anything but the cache.

Stress factor will of course affect the current heart rate but will not affect your max heart rate at all. The max heart rate is the limit of how many beats per minute your heart can beat. 

If the heart beat was recorded properly that means that you ran most of the time with a heart beat of 186x103%=191. It is more realistic as you say to run at a Marathon at 85% of max HR but if 191 bpm is 85% of your max HR then your max HR is 225. 225x0,85=191. Either your Max HR is much higher than you think or the data readings is wrong. I mean The threshold is about 90% of HR max and you can’t run a full Marathon above your threshold. 

Every persons Max Hr is individual and if you want an accurate one you can’t just use the 220-age formula since it might be way off what you have; it is very generic 

I suggest that you do a Max pulse test by your own or take a professional measurement to get things right 

I am afraid it didn't work, the max heart rate keeps being updated although the auto function is off. I have the automatic lactate threshold feature on, is it possible that this also affects the max heart rate? I just saw this post so maybe that's what's happening?

Your comment about stress not affecting max heart rate makes sense to me and I also believe that data readings during my marathon was wrong. I don't think that training for 8+ months with the watch, including threshold and VO2 max workouts, with a consistent max heart rate calculated by the watch should change just because of a single race. 

I could of course do the max pulse test on my own, but that's exactly the issue: if have the auto detection feature off, but the watch keeps updating it to the value based on the readings from the race. I just commented below that in this post someone has this same issue, but they're asking if having the auto lactate threshold on could be affecting the max heart rate as well. 

It might be worth checking that the settings are the same on both the watch and the phone. I have seen, on rare occasions, a difference  between watch and phone settings.