I received this "helpful" email from Prosper:
Thank you very much for reaching out, we appreciate you and your time.
We use Sovos a 3rd party tax vendor. I just wanted to provide a little information on box 3 of your 1099 B.
"Collectibles" are considered alternative investments by the IRS and include things like art, stamps & coins, cards & comics, rare items, antiques, and so on. I hope this helps out!
Please feel free to ask any more questions if you have any.