Strange Lovelace UI bug with unavailable Roku

So this morning I call up my Home Assistant panel in Firefox, and none of the cards appear - only the badges. That’s weird, I haven’t changed anything! I tried an older version of Firefox that also previously worked - same thing, no cards. Tried the UI editor - same thing, no cards. Everything else works, but no cards.

Then I tried the Chrome browser instead, and it’s fine - all the cards appear. WTF?!

The last change I made was to do with my Roku 2 box. It’s normally on rarely, only when I’m using it, but I see a Roku in my list of entities, so HA must have discovered it at some point when it was on. Just out of curiosity, next time I had the Roku on, I added the Roku card to the Lovelace UI, and verified that it works to control Play/Pause on my Roku. Slight bug: only a small square appears for the control that doesn’t change state between Play and Pause, but it works. After the Roku was turned off, the Play/Pause square disappeared, but the card remained otherwise the same. The next day when I restarted the UI, the card had turned red and showed a couple of lines of yaml instead of the Roku controls, but everything else was fine, and since the card was off the bottom of my screen, I didn’t bother removing it. A couple of days pass like this, and suddenly this morning my UI won’t display any cards in Firefox! Logically considering that the red card for the Roku might have something to do with it, I deleted it from the UI using the editor in Chrome. Firefox then worked normally.

So a couple of issues here:

  • I can understand why the button might disappear from the Roku card when the Roku is off, but why does the card suddenly turn red and show yaml a day later? That’s not like any of the other cards when they can’t contact their device.
  • Why does that red card suddenly kill the display of cards in Firefix - and not right away, only after a couple of days?!