Have you also found the OHR completely useless with 18.X/ 19.X/ 20.X?

Yep - the pace average (started with v17 i think) is very annoying and makes it near impossible to run a set pace now as the averaging is over such a long period.
Previously it was a few seconds, now its nearer 20.

I got the updated firmware as soon as it was released.
As a mid distance runner I ran two races (Cross country 10k championship, 5k road race). For those races the heart rate recorded, was in average quite lower with other races I have ran this year, but for me it was max effort. 
Then I have also completed some interval training (400 repeats, 1000m repeats)...total chaos there.
In some easy runs the sensor works better but still there are obvious issues.

18.22/18.23间歇训练（400 次重复、1000m 重复）......完全混乱。

Here is an update from my side: I ran a steady 6:45 on a straight run yesterday and then increased my pace to 4:15 and held it for 1 minute. My heart rate, which was definitely around 175, was almost completely ignored by the watch. Only at the end of the minute, when I went back to walking pace, did the watch realize that something had changed.

I'm so mad that that this thing even made me shave off my few arm hairs to rule out this error too. Garmin support, which I have also contacted in the meantime, says there is no problem and that I should wear the watch properly.

A new day, a new suggested workout from Garmin. 40 min "Basic" run at 7:00. I'm running along and as I'm totally untrained at the moment, I think the heart rate of 130bpm can't be right, it feels higher. So I stop to measure the correct value manually and suddenly the watch also realizes that my heart rate is actually over 150bpm. At this point, I really have to say that the heart rate measurement of a cheap MiBand works better. 

All, 

Thank you very much for your feedback so far on the Optical Heart Rate performance. In addition to what is already mentioned in The Heart Rate Sensor on My Garmin Watch Is Not Accurate, I want to add a few steps to ensure that you're receiving the best wrist heart rate performance. 

• Try tightening the watch to ensure the sensor has good contact with your skin. A snugger watch fit is preferred for activities. The watch should still be comfortable to wear.
• Try wearing the watch on your opposite wrist. Signal quality may improve on the opposite wrist, and may improve performance.
• Warm up prior to your activity. This will increase signal quality by enhancing blood flow and ensure your activity starts with a strong, accurate signal.
• When your activity begins, refrain from frequent adjustments to the fit of your watch on the wrist. This can reduce the quality of your heart rate signal, when the sensor is repositioned or the sensor lifts away from your skin.

Please test these suggestions out on your next few activities. If the accuracy is not improved, please now reach out directly to Garmin Product Support. Feel free to share the results here as well, but we will need to add you to our current internal report for further investigation. 

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I am sorry it sounded like I assume everyone is wearing their device incorrectly. That is not the case. I wanted to point out that it is important how you wear the watch, among the other tips I listed. To some users, those tips are already part of their routine and they are still seeing inaccuracies. That's why I asked for users to reach out to support, so our agents can view everyone's examples of those inaccuracies and get them reported. We are looking into a report of all of these examples and are in the middle of reviewing them and seeing if we can approve. I see in your chat with Support that we did not get any examples, and we need those to add you to the investigation. I will send you a message to make sure you're added to our investigation, but request that everyone else reaches out to get those examples to us!

Hello, yes, that's how it sounded to me. But English is not my first language and I misunderstood, sorry for that. Anyway, I don't want to be part of an investigation team and I don't want to give permission for my connect account to be reviewed.

I basically can't prove anything I'm claiming because I don't have a heart rate chest strap yet. So even if I find out for myself that the OHR completely ignores my heart rate spikes during interval training or is way off at times, I can't prove the true value at that time. Somehow I find "trust me bro" a strange source here. I mean, heart rate is a core function of the watch on which so much of the evaluation data depends.

After clicking through the previous beta program bug reports and the forum in general, I realized anyway that it was pure coincidence that the OHR has worked so well for me so far. And since this is a recurring theme throughout all versions, I have now decided to buy a heart rate belt to at least put this particular problem behind me.

I mean, after so many software versions, the watch still randomly crashes and restarts itself. But that belongs elsewhere.

This is my HR graph, swimming yesterday - suddenly not naturally changed in the middle of the activity (no, I am not a swimming robot ;-) ) My HR graph