Hey there davide42,
Thanks for reaching out to Apple Support Communities. I understand you’re experiencing some issues with the Apple TV app on your Samsung TV and Fire TV stick. I’ll be happy to help.
For both devices, make sure the latest firmware has been installed. You’ll need to refer to the manufacturer for info on how to do this. Also, check to make sure these devices are supported using the steps here:
Devices you can use with the Apple TV app and Apple TV+
If you’ve changed regions lately, make sure the Apple TV app is available in your area:
Availability of Apple Media Services
You mentioned removing the app from your devices and reinstalling, see if resetting the app has any impact on this. This article has more info:
Set up the Apple TV app on your smart TV or streaming device
Regards.