This is one of those things I know just enough to be dangerous. I'll defer to @Tivoburkee who probably knows more.
The voice remote with TV controls is both an IR (infrared) and RF (Wi-Fi direct in the case of Roku remotes) remote. When it's not paired to anything or when the thing it's paired to is off it will transmit via IR. Since the Streambar responds to IR remotes suddenly it will seem as though the remote is paired to the Streambar, but it really isn't; it's still paired to the TV. How to get it out of IR mode and how it got there in the first place I couldn't say, but pairing it to the TV again should fix it. Unplugging the power for a few seconds and plugging it back in would probably do it as well.
I have a similar situation with a remote that's paired to a stick, but there's also a Streambar connected to the TV. I generally turn on the TV with the power button on the TV. If I pick up the remote and press a button, the Streambar will wake up and switch the TV to its input. I have to make sure I cover the remote when I press the first button so any IR signal is blocked. It then communicates with the stick and stops transmitting IR. I think I have the same issue using the remote to turn on the TV, but believe it or not I almost always use the button on the TV to turn it on.
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