Default [Q] Permissions on /system/xbin/su reset

While I was sleeping last night something came in and reset the permissions on /system/xbin/su and cleared the SUID bit (permission bits went from 4755 to 0755). Has anyone run into this? I am concerned that Verizon / Samsung may have slipped something into a product update. Short of doing a reinstall of MI9, is there anything I can do to fix this? Thanks!

(Verizon Galaxy Note 3, rooted with Kingo, still on MI9)

(Edit: I did accept an update to ChainFire SuperSU Pro V2.00 a few days ago. I did not update the su binary. Things ran fine for several days afterwards.)