I have one that was due to pay off on June 12. The borrower posted a manual payment on June 21, and it failed on June 23. It still says payoff in progress, and I've complained three times about it now.
The borrower says she's ready to pay it off from a new account, but hasn't received a response from customer service. After reading MsTabby's notes, I would imagine that Prosper can't figure out how to accept a new payment when the loan shows payoff in progress.
Unbelievable.