I believe those are the same gate. They stopped using U gates some time ago and converted all non-Schengen gates in T4S to 'S' numbering from S1 to S57 IIRC. There are also Schengen M gates in T4S some S1XX gates that are downstairs that I've never actually gone to see. I'm not really sure how those work since I've never been down there or if they replaced the M gates with those new S gates.