My next door neighbors roku remote is affected my roku player. We don't have the same one I have the roku ultra 4K with way more features but I have disabled a lot of them. Every time she goes to get on her Hulu app my player tries to go to the app which exits me out of my app. Since I don't even have Hulu it asks me to add the channel. I don't see how her remote is able to work with mine because it's not paired with my player and she is also able to change the volume on my tv. I feel like messing with her tv tonight. I don't know. We don't know what or why we are able to but according to roku you shouldn't be able to without the remote being paired.
The neighbor could be paired to your roku ultra without you knowing it, but she couldn't be able to control the non-roku tv volume. Unless they have Roku soundbar or streambar, then they can control the tv volume by hdmi-cec. Its wifi signal to your roku ultra and then the ultra sends a hdmi-cec over the hdmi cable control whatever tv its connected to. If you want peace, get together with the neighbor, unplug your roku as she re-pairs her remote to the their roku. Once done have them unplug their roku when you re-pair your roku remote to your ultra.
If it isn't the roku wifi remotes controlling each others roku, it has to be some type of IR repeater system like the old x10, rca, or radio shack pyramids, if you have something like that installed, the neighbor doesn't have to have same type of system, it could just be URC RF universal like mx-600, mx850, RF10,20,or30 remotes which communicate directly with pyramid receiver without the need of a transmitter.
Had to change my WiFi password now it works fine no glitches.