HRM Pro + Running Dynamics

Ah, that may be it. I think I remember seeing it say it was connected after it had already been connected.  I will check for a duplicate connection the next time I run, thanks!

Another thing to verify is that you don't wear it upside down. It has happened to me a couple of times, probably I was tired or stressed and should have stayed home instead of going for a run  

He can do both at the same time: stay at home and go for the run with the HRM upside down. 
But I also did that, changed it while running. 

Yep, I did do that... definitely wearing the right way.  I'm going to run later this morning, so my first thing to do is double check that it's paired only via ANT+.   

Well, I'm happy to report that this morning's run included the full running dynamics again!  And you were right, basically.  Although it was paired via ANT+ to my Garmin watch, it was also pairing via Bluetooth to my iPhone, so I just told it to "forget" the connection on my iPhone, and now it's working again.  So apparently, you can't have the HRM Pro paired via Bluetooth at all, even if it is paired via ANT+ to the watch?

That doesn't seem right.  I thought the Pro was capable of simultaneous "dual channel" broadcasting via ANT+ and BLE so you could have your watch/Edge and a treadmill/trainer record HR data at the same time.

The strap is capable of transmitting HR the same time on both channels. For running dynamics, someone wrote it is only possible to receive it on one device at a time. It is for sure only transmitting this via ANT.
You can have the strap paired via BT even if you are using ANT+ to connect it to the watch (paired in the meaning of it is paired via an App, for example Connect Mobile and listed in the BT list on your mobile) and you will normally get RD data on the watch. I do this all the time im using it, most times the phone is nearby and i don’t cut connection to Garmin Connect Mobile. 
If you are using Virtual Running under these conditions, it will transmit RD data

https://connect.garmin.com/modern/activity/6107129110

I did never take care of the combination of connecting to Zwift via BT and to the watch via ANT and recording on the watch because Virtual Run is older than i own a HRM Pro. I Can’t find a Run were i recorded with Zwift and the watch but did not use Virtual Run.

Thanks to those who offered up great ideas for me to check, but alas, none bore any fruit.  My new EPIX 2 recorded the HRM-Pro running dynamics data on Wednesday JUST FINE, but then two different runs today lack at least the vertical oscillation and GCT data.  Today's run activities show the HRM-Pro battery to be highly charged, and I'm quite certain the HRM was worn right-side-up, the sensors were moistened like I always do, and the band was as tight on the same location on my chest as it has ever needed to be before. I can't swear to having seen the watch display the pop-up "HRM Connected" on either of today's runs (I rarely see it), but I think that's kind of a silly human interface because if you're not looking at the right time, you won't see that.  I'm kind of irritated, because I was trying cadence experiments today, and was eager to see if it improved my vertical oscillation.  I wish there was a way to inspect the FIT file to see if was captured but then lost on Garmin's servers.  If anyone has other ideas for explanations for why something that was working would stop, I'd be most eager to hear.  Best regards.

I do not have Epix 2, just the Instinct 2, but when I use HRM-Pro, I have two additional screens with the running dynamics data in the Run activity, so it is very easy to see whether it works or not, before it is too late (just scrolling down). I'd tell it should be similar with Epix 2 + HRM-Pro. If not, I guess, you can customize the screen yourself, adding some of the RD fields to one of your Run activity screens.

Once you can check the functionality of the RD in this way, and experience problems again, you can try disconnecting and reconnecting the HRM-Pro.