Same thing happened to me. Old MR points expired due to inactivity, so I had a zero balance. Then I transferred SPG points to MR because I wanted to redeem something but changed my mind and the transferred points expired at the end of the month. Called MR and they reinstated the points, but the takeaway was that the system is set up to do this.I was told to use the reinstated points immediately or transfer them back to SPG. if you don't have regular MR activity, better to let SPG points stay with SPG, not with MR.