Model # 4800r. the problem happened from the very start 6 months ago and every time the power goes off,
That device only came out in October 2020, and only 7 months old at the most, so it's under warranty. Do get your receipts together in case a warranty replacement is the way to go.
It should not be doing what it's doing, and you should really have reported immediately. I expect one of the Roku employees, @RokuDanny-R, @RokuMary-F, may need to step in and help. They may suggest steps you've already done. They have to, so go along and do the steps they suggest.
When you state that you lose power, do you mean you no longer have power in your house? How is your device being powered? Is the device plugged into a surge protector, or is it plugged directly into a wall outlet?
With more information we will be able to assist you further.