Side to Side Taper on Base Plate After Surfacing

From center of base plate left and right to about 2 inches its relatively flat but as it move to either far left or far right i get +.010 on my indicator. I refaced and the same problem is there and was wondering what might cause this issue. Video attached for reference.
Video of Indicator from Side to Side

If you can, repeat that same indiaction but with the dial indicator under the tool or beside the tool. Indicate the same area of the table and see if it improves.
My bet is that it’s a little twist in the gantry beam, which a few of us have seen. Mine manifested the same results before I remachined some surfaces to true it up.
Edit- Keep in mind as well that the amount of error you’re seeing is being multiplied because of the distance between your dial indicator and the X axis rails. Since you’re indicating roughly 8 inches or so from the rails it is going to magnify the amount of deflection that is happening at the tool. Hope that makes sense.