Roku does not make the Prime Video app. Amazon does. So any issue you have should be taken up with them. I have 10 Roku devices and I have absolutely no issues with the Prime Video channel. But one big factor is you are using a Roku 4400. That device was released in 2015 and discontinued in 2016. So it’s roughly 7 years old. it’s no longer manufactured. It still gets updates but you would benefit from upgrading to a newer Roku’s model. But the fact that it’s only happening with the Prime Video channel means the issue is on Amazons end. Prime is also showing outages. See link
