I'm sorry, my what? My mailbox number?

Note above since this forum doesn't allow editing of posts: When I press the "Back" button on either the stock Fire Stick remote or the Alexa Voice Remote Pro, they work instantly and immediately, but on the U1, multiple presses are required to navigate through streaming apps.

Okay, so just an update to this issue is that I have come across some related issues that may or may not be an inherent flaw with the remote itself: The first is in my Fire Stick device. The "back" button works, but I have to hit it sometimes 5 or 10 times (whether pointing at the TV or not) before is works. I have tested this on the stock remote as well as the more advanced remote Amazon created for the Fire Stick that I purchased about a month before buying the U1, which is called the Alexa Voice Remote Pro. I will try to keep track of any other buttons or functions I find with the U1. Don't get me wrong, it's still a great remote, and I am hoping this is just a matter of maybe using the "Learn" function or perhaps finding alternate devices in the U1's database for the stock devices that the U1 app chooses by default when I program the remote.

Hey, @e1miran, thanks for the answer! Your tip worked perfectly; not just for my Fire Stick, but for my cable box. I can now control the volume of my home theater receiver within both devices. Thanks!