Vudu unable to play UHD movies on Firestick

[Steve]

Hello. I recently bought a new 4K Firestick and sideloaded Vudu. I frequently use Vudu to watch digital copies I own.

For the first few days using it there were no problems at all. It would stream any movie I owned whether UHD or HDX and Dolby Vision and Dolby Atmos worked perfectly. Then one night it suddenly would not play anything in UHD. When trying to start a movie I get an error message that says "Encountered problems during playback. Please try again." It will play HDX movies with no problem.

Here is what I have tried so far to resolve the issue:

Unplugged Firestick for more than 30 minutes and plugged it back in.
Unplugged modem/router and plugged it back in.
Switched my Firestick to a different network connection (my router is dual band).
Force stopped Vudu and cleared the cache.
Uninstalled and reinstalled Vudu.

The network signal strength for my Firestick says "Very Good." The router is in the next room about 12' away from the Firestick.

I got this particular Firestick on July 18th and have had no previous problems with it. I made no changes to any settings prior to the start of the problem. Note that UHD content plays just fine through Netflix on this Firestick. Also note that UHD movies will play just fine on Vudu on my Xbox One X or my TV. I realize I could just watch through the Xbox or TV, but I prefer the Firestick because it's the only way for me to get Dolby Vision and Dolby Atmos at the same time. My TV is a Vizio P65-C1 from 2015-2016 and does not work with the low latency version of Dolby Vision that Xbox consoles use.

I realize that Vudu isn't officially supported on an Amazon Fire device but that doesn't mean there isn't a solution to my problem. I posted about this on the Vudu forums a few days ago but my thread went off topic and got locked. A member there reached out to me via PM and informed me that his experience is the same as mine, so maybe this is something deliberate by Vudu? Their only response is that Vudu isn't supported on Amazon Fire.

Thanks to anyone who can help.