Very interesting:
If I split the list in two halves then both halves work.
Back to my non-working list: I tried removing just one randomly picked entry and it made it work.
So I thought this randomly picked entry might be suspicios, so I added it to another, previously working list -> It doesn't break it. Still works.
Once again back to my non-working list: I tried removing another randomly picked entry and it still doesn't work.
By the way, the results are always repeatable. A particular list that fails always fails no matter when or how often I try t load it. Another particular list that works always works. So it's not just a random glitch which might make me think certain things work while others don't.
Very strange.