Typically knock off brands like that are going to be thrown together, very little QC. But unless the plate is cast wrong its something simple like the disk-plate isn't seated right, have you tried to re seat the plate?
if not
Take the shield off, loosen the set screw and re set the plate square.
I have sanding disks that are very old, the adhesive has gone bye bye,,I use 3M Spray 77, they stick fine after that
good luck