So this was a mates experience over the last month on a set of 2014 SIDs. Said mate runs a bike shop, is a decent mechanic; basically knows what he’s on about.
Just as you describe, he had exactly the same thing where initially the forks would drop a fraction when locked but they were going to 30-40% now, albeit a bit stiffer.
Sent back off to sram tech who said it’d been checked and it was fine. Got it back, no different.
Sent back again, where they said it’d had the damper swapped out and it was the same and all fine. Got it back, no different.
Sent it back a third time, spoke to the guys on the phone about it before it was sent back and said that if it came back like that again, he’d send them off to tftuned and send them the bill. Magically, the forks came back fixed.
May be a coincidence, and I may be a cynical bugger for thinking anything else, but it was a very noticeable difference.