iPhone 8+ Slow Motion Problem

I recently purchased a brand new iPhone 8+ from Verizon. I remember that the phone should be able to record 1080p 240fps for slow motion. I tried testing it out, and for some reason, the quality does NOT look like 1080p. Regular video quality looks normal, but it’s just the slomo that looks really bad. It’s blurry, and looks more like 480p quality. I’ve gone in different lightings, changed up the settings, restarted my phone, even spent hours with customer support and nothing has seemed to work. I’m at my wit’s end trying to figure this out.

Oh, and another thing I’ve tried: I took two videos in slow motion, 1080p 120fps, and 1080p 240fps. I compared them side-by-side. And the 1080p 240fps looks significantly worse than the 120fps counterpart. I decided to put both the videos into iMovie, and tried uploading them to YouTube from there. The 120fps video uploaded in 1080p, like it was supposed to. And it looked like 1080p. But the 240fps video said it uploaded in 1080p, even though the quality looked much worse than the other one. I don’t know if I have a defective phone, or if it’s just a bug.