What model Roku do you have? The model number, please, not just the name.
I just checked my Ultra, and the Theme menu option is still there, right below Remotes and above Display. There is still a switch for seasonal, which I have turned off. I will say that I have seen it turned back on with an OS update, but not commonly. I never saw any of the seasonal themes, since I have them turned off.
What channel is restarting while in use? Yes, the first troubleshooting step is to remove the channel, reboot the Roku (critical step that must not be skipped) and adding the channel back.
If you're having issues with multiple things, sometimes a complete factory reset clears out some bad code. I don't like recommending it, since it takes a little effort to set it back up. But it is usually successful if the problem is code related. If there's a hardware issue (certainly a slight possibility), then nothing will resolve the problem(s) other than replacing it.
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