49rFaithful
That previous post was very specifically in regards to the P+ app on FireTV/AndroidTV/GoogleTV (its the same P+ app on those three platforms because those three platforms are in fact the same platform) - not the P+ app on RokuOS.
(RokuOS is a completely different OS/platform and therefore the app design is completely different)
You need to check the P+ app audio track selection to verify the Atmos track is selected on each/any/all of your FireTV/AndroidTV/GoogleTV devices - its saved per app per device.
(Several of you stated you no longer had P+ Atmos on your FireTV/AndroidTV/GoogleTV devices - its most likely due to the fact that a P+ app update etc changed the default track to Dolby Digital+ instead of Atmos - therefore you should MANUALLY check and change the audio track to Atmos as described in the previous post)
NOTES
1) The loss of Dolby Digital+ (EAC3: 5.1 & Atmos) support on the RokuOS P+ app is limited to the RokuOS P+ app ONLY (P+ DD+ (5.1 & Atmos) support is fully provisioned and working on FireTV/AndroidTV/GoogleTV - manual configuration as described may be required).
2) Dolby Digital (AC3: 5.1) support is still working for the RokuOS P+ app; however, it is only available for some/limited content, and only when DD (and not DD+) support is detected (via HDMI EDID).