According to the Dell Reward Points Missing Mega Thread,

https://www.dell.com/community/en/conversations/customer-care/dell-reward-points-missing-mega-thread/6a202f8baecd2d485b34a426

Dell performed a program update at the end of May. This update incorrectly caused all of my Dell Reward Points at the time to be redeemed. I did not redeem them myself, and the points were not about to expire. Please review my points and undo the redemption caused by the program update.