955 does not lock to heart rate in the beginning of the bike ride

Unfortunately, no. Garmin broke out the optical heart rate monitor and is happy. And any attention to this problem is a lack of warm-up and a badly worn watch xD

Maybe in two years they will fix it.

Don't flog the messenger, but based on many Reddit comments and my own experience with the FR955, I have learned that the watch's internal optical HR sensor is not accurate for bicycle rides. 

You are best served pairing an external chest strap to the watch and using that for all activities.  I have been using a Polar HR10 and have had no issues capturing an accurate HR while cycling, whether indoor or outdoor cycling.

H10 is a nice strap, but why are you need to buy&use such an expensive watch? It works well with Edge xxx or simply some cellular :)

That's just it.  After years of cycling with a Garmin Edge head unit, I already had the Polar HR strap.

But, after buying the FR955 in 2021, I read many posts referring to the watch's onboard optical HR inaccuracies during cycling activity.   I have also experienced it with indoor cycling.  Note that I do not use the watch for outdoor cycling; I prefer the Edge.

My guess is that Garmin continues to develop a more accurate HR sensor with each new watch generation.  For example, the Venu 3 has a much-improved sensor over the 2.

Also, this may be a general physiological limitation of using the top of the wrist to sense HR. A strap wrapped right above the heart is undoubtedly more accurate.

I think the first time I noticed this was on a Feb 10 ride. It's hard to say what version I had at a time. I usually receive new versions in the beginning of the public rollout. If not 18.22, it probably was 18.15. I remember there was  another 18.xx version before 18.22.

18.22 claims to improve HR senor in the cold weather. This sounds suspicious. My rides were around ~50F degrees. 

Regarding wearing a chest strap, I totally agree. The watch is never fully accurate. But I don't really need accuracy, just consistency. I'm not an athlete and don't have training plans. All I need to know is how hard it was compared to my previous activities. And up until recently 955 worked well enough in this regard.

I know a few very obvious bugs that I can reproduce consistently:

• Don't swim wearing the watch in the middle of activity. It'll throw coordinates some half a mile sideways and will take miles to correct it later
• Don't make a new route and sync and start in the middle of recording. It'll damage recording, it will not be saved
• Don't hope Explore will ever properly support 955. Just make a route, convert to track, add to collection, sync, wait a minute, use it.
• Don't ever hope selecting a point on the map on 955 itself to route to. Use some other means.

I learned to avoid these. Now if I need to take the watch off the wrist right before the ride, wait for HR to zero, put it back, I can do it. This is still easier than wearing a chest strap, remembering to charge it, deal with external sensors, etc. BUT I did not need this before, so it looks like a recent regression and I'm unhappy.

Also what is "warmup"? Is Garmin saying I need to ride loops on the parking lot before going on a 6 hour ride? Why is the beginning of the ride not a "warmup"? I don't really sprint right from the start.

An example of the ride when Garmin did not record the HR properly in the first half an hour. Then I took the watch off the wrist, put it back after a minute and it locked to the right one. The first 30 minutes were all going uphill. I'm sure my HR did not jump instantly like that.

There is an argument to be made that this has been a case before 18.x releases. Here are graphs for one of my last year ride. I clearly did not stop and the HR behavior in the beginning cannot be right. Although it lasted for a shorter period of time. Maybe now the "lock" takes longer, and so we see more complaints? 

Exact same issue running. Starts low and remains low and then jumps to the actual heart rate 10-20 mins in. Hasn't always been the case. I'm thinking it started with the 18.22 update.

I had the same issue. I changed my watch on Support and leave Version 15.19 on my FR. I will try next week, if it is better. There are coming no fixes....