I also have YouTube premium and watch mostly on my iPad and TV. YouTube constantly logs me out at least once per day. I notice because I’ll randomly start seeing ads again (I open videos from my rss reader, never their site). This never happened when I wasn’t on premium. I don’t get what they’re doing, but my impression after almost a year is that it’s only slightly less annoying than getting ads. At this point, I might as well not renew and just use ad block.