Why does Apple TV 4K keep buffering on photos app

I’m trying to replay my 1 hour 26 mins 4K video on it and every 3-5 mins it’s buffers and please don’t say it’s my internet like the other post as I just checked “Speedtest” and I’m getting 526mbs downloads speeds. Other streaming app are fine but only buffers when I try playing my own video. And the Apple TV is wired up with the Ethernet cable.