Partial Source: The Wrestling Observer Newsletter
UPDATE x 2: According to one source, the reason that WWE booked Ryback to hit his finisher on Big Show on WWE RAW a few weeks back, only for Big Show to kick out and then beat Ryback moments later with his Knockout Punch, was possibly due to their frustration over Ryback using Bill Goldberg's spear and jackhammer during a recent match without getting permission ahead of time.
UPDATE: As reported earlier, Ryback reportedly has "nuclear" heat on him backstage in WWE right now. This has lead to his recent losses on TV, including one to R-Truth, who is clearly seen as a mid-carder. They've also scratched the storyline that they had planned with Heyman and Ryback.
According to sources, the heat is due to several issues as we noted in our original report (see below). In addition to those issues, Ryback performing Goldberg spots (such as the Jackhammer and the spear) during matches without getting clearance from officials first is another reason for the heat. WWE officials were not happy at all about this and confronted him backstage about it.
ORIGINAL: We reported last week that Ryback currently has heat on him in the WWE. He lost to R-Truth last week in the UK and last night he lost to The Big Show, which saw Show kick out of his finisher. There are said to be issues with his ego and attitude. Also, the company is not happy with Ryback's lack of progress in the ring. The angle with Paul Heyman was also considered a complete flop. We'll have more on this shortly.