This is "nicht gut"!
Key question: Is the "emergency stop" still activated?
To be honest, since you mention it is in the rear (and since this part my get a bit more dirty when folding down the rear bench every once in a while), it is VERY likely that this is casued by dirt.
Would it be a non-warranty issue, then I would strongly advise you to clean the belt with a bit of soap.
Yet, as Derek hinted, this is likely to be covered by a warranty, so do take the drive to the dealer.
Will you let us know what it was? (always curious to learn)