Problems adding Aqara Door and Window Sensor P2 (connected via Echo/Alexa)

I finally picked up some of these to try Matter/Thread out, but don't seem to be able to connect the device to HE.

This is a thread device and connected to Alexa via my Echo 4th Gen, and seems to be working in Alexa app (I see open/closed events on the contact sensor device).

In Alexa devices, there are 2 new devices:

  1. "First device" (Aqara smart device, Type "Other") connected via Aqara
  2. "First contact sensor" (Aqara smart device, Type: Contact sensor) connected via First Device

When I select the option in the Alexa app to add another assistant/app from the settings on either of these, it gives a pop-up that both devices will be added to other assistants or apps.
Select OK, and it generates a code.

On the C-8, I enter the code (without the dashes, because the UI doesn't seem to accept them), it begins search for the device, and after a few seconds it displays the message about "having trouble pairing your device". From here it just spins seemingly forever (sending a status request to the hub every 1s; well past the 15 minute timeout on the Alexa app).
No logs appear to be seen on the logging screen for any of this.

I reconfigured the Network setup to be as simple as I could:

Router: Deco X55 w/ IPv6 enabled
Echo connected to Deco wifi network
C-8 (Rel. Connected directly to one of the X55 ethernet port

Is the C-8 expected to work with matter/thread devices connected via Alexa/Echo?
Is there something about this particular device that causes it to not be found by HE?
What steps can be taken to troubleshoot issues adding Matter devices?

The first thing I'd do is check Settings > Matter Details to see if you have a device in that table that looks like it might be this one. Assuming it doesn't work (if it does, I guess you're already good...), remove it and try again.

I've never used Alexa for this but know it's been tested, so it should work. If Alexa provides you a way to see a list of other connected services/fabrics/admins or whatever it may call this feature, seeing if Hubitat (or likely "Matter test" or whatever numeric ID this corresponds to -- I don't think it's certified at the moment so has to use one of those) is listed there and removing it if so may also help.

You can also try the old-fashioned restart of the sensor itself (e.g., remove the battery), perhaps the Alexa/Echo device itself or whatever your TBR is, and if nothing else, a reset of the sensor and starting the whole process over if that's not going to disrupt anything you already have on Alexa.

Settings > Matter Details shows nothing (the process doesn't seem to get that far).

Restarting the Echo (TBR), resetting device (using the reset button), removing battery, deleting the device and adding back to alexa all have resulted in the same behavior described in the first post.

Odd. For other failures, there's normally an error code (and description) that would give your more information, but yours seems to just be getting stuck...

Maybe others will have more ideas.