My Up Next frequently ends up in a state where it is missing several shows. Sometimes it displays everything and then some will just disappear. They aren’t hidden and will come back in a day or two.
For instance that there’s a new episode of The Voice I have not watched yet:
But it appears nowhere on my Up Next:
And it’s not just one show - there are maybe 6 or 7 missing. And there doesn’t seem to be any consistency between which ones disappear.