chest strap HR monitor?
Are you suggesting he's got consistently erroneous HR data rather than considering these figures are feasible?
Plenty people have used multiple sources of data on a multitude of training sessions and races under varying conditions spanning years and seen consistent data in these ranges. Not spikes, or cadence lock incidents. Not unpredictable or inconsistent with perceived effort or pace. Why do you insist this is not true?
What is your max HR and typical HR for a selection of running or cycling race distances?
Over 10 years ago I measured a HR over 200bpm on several credible occasions and a max of 203 or 204. These 200+ values were always consistent with an all out effort and displayed a normal rising curve lagging the exertion followed by a normal looking recovery. I have on rare occasions had spurious results, these look quite different and are easily dismissed. These days my max HR is somewhere around 190 but that's expected as max HR does drop with age.
I've used 4 different Garmin chest straps from the old hard plastic "classic" strap, to the Tri and Swim straps that were bundled with the 920XT in 2016. For the last couple of years I've been using a Scosche optical sensor and again the data is completely consistent with all previous trends.
The friend I mentioned in a previous post who has done half marathons and marathons with very high average HRs has used a similar selection of Garmin sensors and also currently uses an optical Scosche. I've seen his data going back about 11 years IIRC and I've no reason to doubt it's accuracy.
You'd be right to query a poster who appeared to be jumping to conclusions based on isolated values from their watch. What you've got here is several people with consistent data over many years telling you that what you think is incredible is just incredible to you, because it's not been your experience.
To clarify, I'm not saying the OPs observations weren't equipment related. I think it's quite possible given what he's told us that it could be "cadence lock". However you seem to be arguing that such HRs are impossible and that's simply not the case.