Reply to Shift button & Deck switch on S4 glitch

I've been through everything I can see on the community s and can't find anything on this (I'll graciously accept if there is something!)

Has anyone else had this problem? When I hit either shift or deck switch to C or D there is a lag in the track...

As I'm using (a slightly modified) version of the Ean Golden mapping, I'm using the shift button quite a lot, and I can hear the lags... It becomes VERY pronounced if I hit shift a bunch of times (yeah, I know I wouldn't be doing it live, but I'm sure it shouldn't be doing it!)

Has anyone else come across this?

btw - fully updated version, recently cleaned laptop (no erroneous programs) network adaptors off - in full "gig" mode running a 2.4Ghz dualcore (M450 i5) with 4gb ram so spec shouldn't be the issue.