Were your SPG nights correct before you merged them? This problem is widely reported. The SPG nights are incorrect in many accounts.
(a) the YTD nights is reported as lower than the total number of actual YTD nights shown in the account history. In my case, when the account was migrated to Marriott my last stay of two nights was missing from the account history. This reappeared a week ago but the two nights were not added to the YTD nights. It's clear there's no link between the account history and the YTD nights. In my case this is nothing to do with credit card nights because I don't collect them but it's a result of the missing stay from end of July that was not added to YTD when it finally reappeared in my history.
(b) the lifetime nights is also incorrect. During the account migration they added the actual lifetime nights and the current YTD nights to make a new lifetime nights total. Many people have reported this. It's not easy to see how and why this would have happened apart from careless human error in the migration script but it did happen. It's also not fixed.