Delayed downshift from gearbox
Hi can anyone shed some light on this one? My bike has covered 3000 km since new and seems to have developed a weird habit of not shifting down immediately from 3rd to 2nd. This is perhaps not the correct way to describe the feeling I'm getting from the gearbox but it's difficult to explain. The bike shifts gear fine and never misses a shift, gear changes are smooth enough, it's just that when down shifting (especially it seems from 3rd to 2nd) after having made the down shift I can feel a delayed click as the gearbox selects the gear a fraction later. It only seems to do it on down shifts not up. I thought perhaps this was all in my head and so let my son ride it (he rides a 2019 MT10 Yamaha) and after a ride of 10 mins or so he confirmed he felt the same. I don't think the bike had this '' problem'' straight out of the box and the only work I've carried out is to replace the levers (Puig folding adjustable) and an oil change (Motul 10w 40 semi synth) both at around 1000 km. which I think is when it started. I've adjusted the free play in the clutch cable following the manual (at the lever end) any chance it could be the oil? Should I switch to full synth and see if this makes a difference?
any suggestions most appreciated