Heartrate so inaccurate that my watch is basically useless for training

Yeah, it is almost like it is a scam internet site. The only solution is to just return a watch that we think that is faulty. Not an elegant solution, but it is obviously the only one.

Adding my voice to this. I purchased my FR265 around March 2023, and the HR was great, though I almost always used it in conjunction with my Polar Verity Sense, an OHR arm-band. I did perform some tests to compare the Sense and 265 HR sensor readings on a few exercises, but focused on rowing, which was very problematic for my older OHR watch. At that time, everything looked great with the 265 HR data.

Fast forward, and after an update, the 265 would often not connect to the Sense, and I started getting crazy inaccurate HR readings. Fortunately. I was able to fix the 265/Sense ANT+ connection issue, so this is not affecting me seriously, at the moment.

This is obviously a software issue as many people report, as did I, that the watch was initially very good at tracking HR, but no more. I could go back to my old Fitbit and (now) Google if I wanted that level of service.

Just wanted to add my voice. I've also been having problems with my 265 for about 4 months. Initially it was super inaccurate spikes or dips in the hr data, and now it doesn't even seem to connect to the heart rate signal in general. I'm a miler, and so interval workouts are my "bread and butter". Watch works fine at paces slower than 7 min/mile (I guess?) but anything even remotely close to threshold, much less repeat paces, and the watch doesn't have a clue. Been really frustrated with this total lack of problem fixing from Garmin. Anyone know the accuracy of Coros Pace 3? Thinking about switching if this problem isn't fixed soon or there's continued poor communication on update timeframes from Garmin. Any other watch suggestions for a miler/2 miler looking at about 45-50 mpw's and 2-3 track sessions a week.

Also noticed on this board that some claim that software 17 is more accurate. Any way to switch to this (currently on 18.23), and is it really superior. 

What I noticed is in my scenario soft reset somehow fixed problem but only for some time. 

Coming back to this after the 18.26 software update. I've only done 2 runs since the most recent software rollout, but the heart rate data seems significantly improved for me. It locked onto my heart rate right away, as opposed to the seemingly garmin standard of needing 5-7 minutes, and remained consistent despite several stops/restarts during the run, which also threw off my data in the past. Will be doing an interval workout on the track later today which would typically go disastrously wrong for the 265 hr data. Will update with results. 

Tested the 255 music against the HRM pro plus. Granted, it was a steady state, from walking to running steadily. Apart from a slight lag, the 255 was on par with the chest strap. So much, that I am not going to use the strap anymore when doing just easy runs. I will be testing the 255 during intervals too of course, but this will take some time..

Watch is doing so much better. No idea what Garmin did but the latest software update (18.26) seems to have fixed the majority of the issues. Data looks great on steady runs, but can be a little inconsistent in interval training. Did a speed sessions with 600's, 400's, 300's, and the watch didn't track it super well but was still light years ahead of how the data was looking 2 weeks ago. At least looks like the optical monitor is latching onto something resembling heart rate. Also, only takes 15-30 seconds for the watch to latch onto the hr signal. 

I’m right with you. Took down my response because I thought the watch was finally working but then today decided to not only lock onto cadence, but after that lock onto some completely random signal around 120 bpm. Cmon Garmin.