When we moved in we replaced all outlets with Tamper Resistant ones. We had an outlet on the left side of room that was half controlled by a switch. We wanted both outlets controlled so we left the little tab. It worked fine for a month or so. When we moved a dresser on the right side of the room we noticed an outlet had gotten forgotten so we replace it (it had not been controlled by the switch and was always hot.) As soon as it was replaced the outlet on left side of room stopped being controlled by the switch and is always hot.
How do we fix that? Over time we have found other switches that control nothing and wonder if it is a similar situation.