There are quite a few reports of this today on the US forum - the prob is same we've all used the Echo Show 5 as a clock and now its useless for that.
I suspect that there is cloud based configuration data for each device type so that they can share the same base firmware - to explain why I saw it across two firmware versions, but I cant explain why some people are not seeing this change yet.
My experience is the same. As of two or three days ago, the clock face will not stay on, even if the the setting for continual rotate is turned off. I have also turned off all other displays like weather, stocks, etc, but it still switch from the clock screen to a blank scene with the time up int he corner. Amazon, whatever you did in the last update, UNDO it! Fix this now. I bought the Show 5 as a bed-stand clock and loved it until a couple of days ago.
As a side note, I can get the clock to stay fixed on the screen by going in to setting and saving the 'recent' clock type. But it switches back to rotating to the blank screen as soon as the alarm goes off.
This issue in this post is Resolved. The steps for resolution can be found here.
- Make sure the current clock face is not the first option under Settings > Home & Clock > Clock > Personal Photos > Clock Face, as this option mirrors a mini-clock design. Please select a different clock face.
The resolution was that Amazon reverted the previous change so that with Rotation Off your chosen clock is now displayed full time.
It's worth turning off all item toggles in Home Content as when returning Home after performing an action the echo will first display the following sequence of screens (5 secs each): 1) chosen clock, 2) small clock & try Alexa, 3) any pages you've enabled in Home Content, before finally staying on your chosen fullscreen clock.