Garmin forerunner 955 and Garmin HRM-PRO.

Haven't had that issue with mine since I started using the 955 3 Jul.

I have had issues where it takes 5-10 minutes for the running dynamics to appear. But for some reason the HR does read immediately.

Have you downloaded via CIQ the heart & ant+ data field? 

No issues with mine at all. I recommend you to reconnect strap and restart watch.

Things to check:

1. Are you sure the strap is actually paired and connected?
2. Is it paired over ANT+ or BLE?
3. Are you sure you're not wearing it upside down?

I have similar issues (repeatedly) - the way I fix it, is to disconnect / reconnect the belt from the sensors screen - it then works straight away and doesn't seem to drop signal.

Even if it says connected initially - I always see the optical HRM is still active - then I know its not actually connected

So I was able to find a workaround but it's not ideal as I had to disconnect my headphones which means no music during my runs :( Here's the workaround:
1. Keep the Garmin HRM Pro / Pro Plus paired as ANT+
2. Pair the Stryd as PWR-Stryd paired as Bluetooth.

Occasionally, the watch will power down halfway through the run but doesn't always do it, though all the running dynamics from the Garmin HRM and Stryd stats show.

Garmin Connect https://connect.garmin.com/modern/activity/9325689361

Sadly my watch stopped giving me vo2 max updates even though I've had tons of positive performance conditions over the past 3 weeks. 

I had the same issue.  Removed the HRM Pro form the sensors on my 955, checked the connection was ANT+ ( it was previously) and re paired the HRM and the watch after I rebooted the watch.  Everything seems to be working fine now

Yes, definitely think this is a bug that I hope garmin is putting their attention to fixing in next release.  I want my headphones, stryd pod and hrm pro/pro plus to work when I run and ride!