Actually, that's not true - they were up just a bit at 4:15. Also, you're forgetting about backwardation. It costs $ to roll from the Sept. to Oct contracts when the first month VIX Future is higher than month 2. The daily roll cost works against XIV, and in favor of VXX/UVXY during backwardation. That monthly backwardation % is now at 11%.
XIV tracks a mix of the first 2 VIX futures. It does not have anything to do with the spot VIX. Learn before you invest. The behaves exactly like it's supposed to. You and many others simply don't know how it is supposed to behave!
I'm sorry to be blunt, but you (and many others) need to learn what these products are based on. It is not the VIX. They trade in VIX futures which have their own set of variables that affect the short and long term values of this fund.
There is a widespread misunderstanding about the time and pricing of VIX futures-based exchange traded products. If people don't know how this works, they will claim crazy stuff like "manipulation". That's just not the case.
Here's the deal: Volatility products set at 4:15ET not 4ET because that's when $VIX futures settle. However most % change calculations like on Yahoo will use the 4PM close. Yesterday, those 15 minutes were pretty substantial.
The funds are tracking fine. It's the % change calculation that is not using the right data, so it will lead to confusion.