It doesn't look like it's U521 itself but some other data mess up that's doing this. It just started on or about Aug 8 and U521 has been around a lot longer that that. According to Dish they're working on a fix that will hopefully come very soon.
I’m pretty sure it didn’t start for me until 521, just the other night. But I’ve heard that “hopefully a fix...” for over 20 years now.