HR since v5.0 update

I just received this watch a few days ago, and upgraded to v5.0 as part of the initial setup, so I can't compare to the earlier firmware versions.

I have, however, been fiddling with it obsessively, including comparing the heart rate and SpO2 values to those measured simultaneously with the sensor on the back of my Samsung Note 8. I've found that the resting HR values are essentially identical, and the SpO2 values are 3-5% lower on the watch than on the phone. The resting HR also matches exactly with a manual pulse count using my finger/neck and a wall clock.

I know that this isn't exactly what you asked, and that taking a manual pulse while your "harder runs" are in-progress wouldn't be practical. Perhaps you could take an old-fashioned manual measurement right when you stop running, while your heart rate is still elevated, and see how that compares with what your watch is reporting?

I feel quite the opposite. My HR seams to be about 10 bpm lower after updating to v5.0 ... strange. My Vo2 raised 2 points in a short period, unfortunately I don't have any other device to measure my HR, so I don't know if it's correct now or not. Anyway quite strange situation. 

I agree with 4598970.  Lately, perhaps since the latest update, for the first few miles of each run my heart rate has been through the roof.  Zone 5 when I'm running at an easy effort.  Things seem to become more accurate as the run goes on.  But by then it's too late and all my stats are effected (Training Status, VO2 Max, etc.).

Additionally, I went on my last 20 miler and the screen on my watch froze on my mile 4 split.  It kept beeping at my mile splits until mile 14 but the screen never changed.  I had to force quit the watch at what I believed to be about mile 20 and when I was able to look at the data it had tracked me until approximately 14.5 miles then quit.  Frustrating way to run my last 20 miler.

Garmin has been having some major issues lately, obviously.  I've contacted their customer service in the past with mixed results.  Last time they actually had the nerve to blame me for not powering off my watch on a consistent basis.  Come on, Garmin.       

I've noticed my heart rate accuracy is pretty bad after the update. Any suggestions on a previous version to roll back to?

I have exactly the same thing! My average HR on 5km run is 20% higher than before v5.0 upgrade. I have contacted Garmin with no success. They said can not do anything about that.

PS I have tried downgrade to 4.87 but it was not possible.

Do you have a chest strap to compare readings with? 

No, but you can compare my data before and after the update. Exactly the same place, the same distance:

BEFORE update: https://connect.garmin.com/modern/activity/5464975590

AFTER update: https://connect.garmin.com/modern/activity/5474789229

That's interesting; thanks for sharing these.

I've only had this watch for about 2 weeks, and have only ever run with the v5.0 firmware, but all of my runs list my Aerobic Training Effect at 5.0, 90%+ of my time in Heart Rate Zone 5, and copious spikes above what it thinks is my maximum HR for my age/gender. I assumed that these readings were correct, but perhaps not.

For comparison, I take my pulse manually at the wall when swimming (I haven't swam since getting the watch, due to an injury). When I'm working my hardest - way harder than when running - I can't get within 25 BPM of these numbers. When I'm cycling hard, the watch reports a more moderate HR (usually around Zone 3).

Taking everything on this thread into consideration, and my earlier observation that the watch is accurate for resting HR, the pattern seems to be that the watch is accurate at low HR, and gets increasingly inaccurate as HR rises.

I don't have a chest strap, but I'll try to compare the watch with the sensor on my phone immediately after stopping running the next time, while my HR is still high.

That's quite a difference. Something isn't right.

Mine hasn't changed as much as yours but does also seem to spike, e.g. Sudden jumps from 145 to 165 without much change in effort. Previous readings would never do that.

I don't have a chest strap but I could borrow a watch off someone else I guess. 

Training Effect around 4.5-5.0 and almost permanent Heart Rate in Zone 5 - I have these in all my running trainings now. Plus "Recovery time" around 4 days (before software ver. 5.0 it was max. 24 hours). For me that data are completely unreliable and I think it might be the same with yours. 

Let us know here about your HR comparison with phone.