Just a little FYI, screenshots that do not show the properties that have been modified in the layer in question are meaningless. Nobody can tell anything about your composition or your workflow from the screenshot you provided. Select the layer or layers that are giving you problems, press the U key twice, then take a full sized screenshot and just drag it into the Reply form field on this forum then precisely describe your workflow. I have never seen a mask on a layer offset unless there was some other effect applied to the layer. Never, so there's probably something fouled up in your workflow.
As Rick already pointed out, your info is insufficient. You have not provided any info about your version of AE, sytem, comp settings and so on nor any useful screenshots.
disable any effects on the shot. i had the same thing happen to me. i warp stablized the shot first, which apparently offset the mask. i turned of the stablizer and everything was kosher.