I've seen people say that the free Roku HDMI extender cable
can sometimes help with possible EM interference from the TV. Although, I don't think the cable is very long, so not sure how much it could help.
Are you able to try the Streaming Stick+ on another TV to see if it exhibits the same problem. If it does, it's almost certainly defective.
Changing your wireless router to broadcast on a different channel could be something else to try (only if you're comfortable making changes to your router's settings). I think the remote uses the same channel that the Roku uses to connect to the wireless router. However, if your Roku isn't also having issues streaming video content, you likely wouldn't want to change the router channel.