Aprilia RSV4 gear shift issues

Mar 2013
Bracknell Berkshire
Recently changed from a RSVR to a RSV4R bike is great but just been having an issue with gear changes. All okay changing up just some issues changing down seems like it is having an issue with a return spring on the gear shift not sure but doesn't do it all the time as I said.

Does anyone have an idea of what it could be and what the potential fix could be appreciate the help. BB