Maybe they're just learning about FIRPTA and realizing they take a huge financial hit by selling (if only temporarily). If the seller backs out you don't lose your money. The money being held by the title company would be returned to you in its entirety.
Take a look at your contract and see how far you are from the stated closing date.
If you are past your closing dates, you have the right to back out of your contract and get your money back without penalty. If I remember correctly, you got a really good price on a stripped contract, so you'll want to weigh wether that contract is worth it, or if you don't think you can find equal value in a higher priced (less stripped/loaded) contract.
If you are not yet past your closing date, you'll just need to wait it out. Your seller may get over their reservations and just let go of the points. In the interim keep an eye on the market and see if there is something else that may interest you as a plan B. That way, if the contract does fall through, you won't be caught flat-footed.