Displaying Lovelace dashboards on Echo Show 5

First of all, this question is about the Echo Show 5 device specifically, not the Echo Show 8 or 15.

I want Alexa to show me a Lovelace dashboard in response to either a voice command or an HA automation. Aladic has created a great custom Alexa skill that tries to do this. There is also a skill called MyPage that should work. Unfortunately, although people report success with the Echo Show 8 and 15, it doesn’t work on the Show 5. Both skills work with other web pages, but fail in the same way with HA - leading me to believe the problem is with the the Home Assistant front-end login screen rather than Alexa skill.

If I try to use my internal HA URL, I get a blank black screen. The Alexa skill loads an empty APL template (expected behaviour), but doesn’t then load the Home Assistant front end. I suspect this could either be due to name resolution issues or lack of SSL, but I haven’t tried to debug this.

If I try to use my external Nabu Casa URL, I get a Home Assistant logo on a plain white background (no moving geometric pattern), and the text “Loading data”. After a second, a blue spinner appears. This looks like the screen that normally appears briefly after you enter your login credentials. However, no login prompt appears, and after about 30 seconds, Alexa times out and starts cycling through adverts again.

If I type the URL directly into the Silk browser, the Home Assistant front-end loads fine. Both my internal and external URLs work; I see the normal login prompts with the moving pattern behind, and my dashboard displays after I have entered my credentials. This implies that there is nothing intrinsically wrong with the Echo Show 5 device - it is capable of working properly. However, I’m not aware of a way to automate opening a web page in Silk. The two Alexa skills claim to do this, but it appears they actually open the page in a different environment that doesn’t work the same way as Silk.

How can I debug this? The Alexa Developer Console is no use - it opens HA in my desktop browser, which works fine. And I can’t see any errors in the HA system log. Is there any way of finding out what HA is actually serving up to the Echo Show 5, to see if it is any different to what is served to other devices? How can I tell what I’m seeing is even served up by my HA instance, or whether it has just come from the Nabu Casa proxy? I’ve asked on StackOverflow about the differences between the Silk browser and the web environment used by Alexa skills, but had no responses so far…