In the After Effects render order, masks are processed before effects are rendered (and the effect itself can override mask handling). That means that when you mask on a layer with the Warp Stabilizer effect, you are looking at the post-effect view in the viewport, but masking pre-effect. You can change the render order by precomposing.
Cut your mask. Precompose your P1030736.MP4 layer, being sure to choose "Move all attributes into the new composition." Paste the mask onto the precomp layer.