It shouldn’t show up one day as 5.1 and the next as Atmos.  Though different sources can have different formats.  Example: You can purchase Paramount+ through Amazon Prime.  You can then stream from the Paramount+ app or through Amazon Prime.  The Paramount+ app version is Atmos, the Amazon Prime version is not. 

Your response is logical, but I'm not so sure about this.

Example for me last night Netflix was not showing Atmos availability on shows previously viewed in Atmos. I checked the web for chatter but nothing.  At the time, Atmos was available on other apps e.g. Disney and Apple.

 This morning, all those titles on Netflix were again available in Atmos. I think it had to be a temporary bug in the Netflix signal. Could happen on any app.

As I said, it “shouldn’t show up one day as 5.1 and the next as Atmos”.   I’m not knowledgeable enough of the OP’s situation to be able to say it most definitely won’t. I merely gave an example where it definitely would be different.

Good news is,for me both formats sounded great. 
For music, when I feel the sound is lacking I go to a different provider (Amazon, Apple, etc. ). 
I’ve often improved the sound by moving around. By my second gin and tonic I usually stick with the station I’m on. Cheers…..