Google has been updating the YouTube Roku app, and each time it makes it worse on older hardware. I quit using my Roku 2 XS several years ago because it was unusable on YouTube. Your Roku SE is a couple of years newer than the SE, but still woefully underpowered compared to the latest Roku players. If you can find a Roku Express+ (model 3910), it still has composite outputs but is powerful enough to run the latest channels.
Nvidia Shield, Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.