HR figure soars trying to disconnect from HRM-Tri

Yeah, I have a similar issue with washing the hrm-run after an activity. If the watch is still in range (if I haven’t taken it off) then I get ridiculously high numbers. I have started disabling the hrm-run from the sensors menu after each activity, but the problem is sometimes I forget to re-enable it. Not sure if anything can be done about this, unless Garmin decides to disable the connection to the external hr strap while not in an activity. (Maybe that could be an option: on/off/on during activity).

I also could’ve sworn that the hrm-run only works while you’re moving (which might explain your issue if you pick up your bag and walk around), but I guess it takes a while to time out and go to sleep.

The chest belt should shut itself down after 2 minutes of being motionless, at which point the wrist OHR should come back on. Picking up your bag and moving within those 2 minutes may keep it awake. Checking the status on the watch will actually keep the connection open - if you want to know what is happenning, check the LEDs on the back of the watch. If they are on, the strap has turned itself off.

Might it help if you don't have an activity selected? I always thought the watch only searched for external sensors when an activity was selected as we can see in the image above.

Yes it is a common problem with the watch connecting to a Tri or Swim strap after the activity has been saved. You can confirm it is connected under the system/settings/sensors and accessories then look at the status for a particular strap that the watch has previously connected to.
The watch is always searching for a known strap if not already connected. When connected to a strap that is not worn (in your gym bag for example) you can get a rubbish signal and merrily watch your HR climb to 250 using the HR widget. I don't know about a 2 minute timeout on the strap as mentioned above. It seems a lot longer, maybe prolonged by the HR widget. FRUSTRATING!!!!

Sorry, but why it this an issue? You are not recording an activity so why look at HR? If you really want to check your heart rate recovery then keep th strap on for 2 minutes after you press stop (without saving the activity) and the watch displays it. After that go and have a shower and the strap will be disconnected when you’re out.. or have I missed something here?

When I finish an activity, I save it, then exit the activity to the watch screen. At that point I really don't care, my heart rate is coming from the OHR - the OH sensor is on. Of course, if I open an activity and the sensor is still transmitting something, it'll detect it whether or not it's being worn. But only if I've an activity selected. So, as CW says, what's the issue?

This is what I just did:

Opened an activity.
HR strap detected - OHR lights off.
Started/stopped an activity.
Saved activity.
Exited activity to watch face.
OHR light came on.
Opened an activity.
HR strap detected - OHR lights off...

In my experience

no HR measurement from HR strap after exiting an activty

this already happens.

The OP is not saying the HR is detected after exiting an activity. He's saying an HR is detected from the strap when the strap is not being worn and an activity selected. That's what the image is showing.

OK, it should be known here that OP (me) has been using these Garmin wearables since 2004 and the dreaded brick known as the Forerunner 201, so I'm pretty familiar with the Garmin handlings. :D (and, thinking back, I've upgraded to literally every flagship watch since then -- I should be handed a freaking prize at this point).

OnlyTwo above has a great point with his fact/wanted with the firmware solution.

To clarify some things in my original post:
-- the image was snapped in run mode only to see if I could trick it somehow. The spiked HR happens regardless (e.g. clicking the down arrow while on the clock).
-- The HRM-Tri strap is indeed wet in the bag. I rinse it after the activity because spin is always a disgusting sweatfest.
-- I do always wait 2 minutes before saving the activity to check the HR prompt -- that isn't the issue here.

This could indeed be fixed with an option to disconnect any external HRM upon saving the activity.

And for those asking what the issue is here: I actually like having my data correct in GC. And, even if I know what's going on now when this issue is happening, I still take a manual pulse just to be sure. It's like trying to ignore some fire alarm when someday it could actually be the real thing. I don't care for it at all.

reason why OP went back in the activity screen was trying to confirm or deactivate those high HR values because high values showed in the widget
when I am wrong with this assumption then there is no issue
:)
OP needs to get familiar with the Garmin handlings ;)

To me, this is minor and I think Garmin should spend their time on bigger things like getting training load to sync better between Edges and Forerunners for example. Then again, everyone is entitled to an opinion!