Old Elite trainer, now sending only constant power (but receiving slope input correctly)

I have a 2015 Elite Real Turbo Muin, which I’ve used happily on Zwift since the beta days…

Recently I’ve had various connection problems, which I initially thought was related to a new Windows laptop, or an old ANT+ dongle, and problems were intermittent.

Now problems seem constant, regardless of old laptop or new, old ANT+ dongle or new. I’m able to connect, and when I am pedaling in the Paired Devices screen, my power reading changes appropriately. However, whenever I move over to start to ride, only a single power level is being sent continuously (i.e. my avatar rides endlessly at 200W, or 170W, or whatever power I happened to be pedaling at the moment of leaving the Paired Devices screen).

But communication is still happening! The trainer’s resistance changes appropriately, and on-time (in my experience), with Zwift course climbs and descents. It all feels normal. But either the trainer is sending, or Zwift is receiving, this constant power message.

I started by asking Elite for support, and they said to ask you… Any idea if this could possibly be a Zwift problem? (I’d love to, of course, not replace the expensive trainer, even knowing that it is five years old…)

Thanks for any thoughts, suggestions, or recommendations.