Roku operating system version 10.5 added a new "Power" item in the "Settings > System" menu for some of the latest Roku devices. I don't know if the Soundbar Pro is one of them. If you have the "Power" option, an "Auto power savings" setting there will put your Roku device into a low power standby condition after a period of inactivity, such as when your tv has been turned off for a while. Frankly, I don't see the point of this.
By unplugging and restarting you are taking it out of this standby condition and returning it to normal operation.
If your Soundbar Pro has the Power option in its Settings > System menu, go into it and deactivate any power saving option you find under "Auto power savings" to keep it from going into the standby state in the first place.
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Ultra 4800 | Streaming Stick 4K+ 3821 | TCL Roku TV 43S245/C107X