Just bought a new Roku Express 4K+. Have had it for 5 days and have had to re install both YouTube (not YouTube TV) and Prime Video 6 times. They randomly keep disappearing from my home page. Last night we were watching a TV show on YouTube and the show all of a sudden stopped playing and the screen went dark. When I tried to go back to the YouTube channel to resume the video, once again both the YouTube and Prime Video channels were gone. These are the only two that get deleted, everything else stays. I have done everything I can think of including a factory reset, contacting Roku and Amazon for support but nobody has any answers.
If you are currently using the TV's USB power port, try using the included USB power adapter at the wall outlet.
If you have other Roku devices linked to the same Roku account, remember that any channel added or removed from one device will add or remove that channel from any linked device. (can also add/remove channels from a Roku device by using the official Roku remote app as well, so eliminate any little hooligans/pranks as a consideration).