I think the solution had been found by sdrio in his post of 2 May 2016. He dismantled the clutch, cleaned and soaked all the plates, and reassembled. That eradicated the fault for over a year. Now he has had to do it again. I suspect that this procedure is worthwhile for us all, although sdrio's low mileage exacerbates the problem, since the clutch plates are clamped together for long periods between rides. This increases the inherent stiction and results in either slippage or loud clunk when first gear is engaged.sdrio do you have an update to your problem? How did it go longer term? Has the issue come back? I am having that same problem.
Wet clutches pose several engineering problems, the main one being the type and grade of oil used. As and30ers correctly stated, you MUST check that your oil complies to JASO MA or MA2 specification. This cunning blend provides lubricity but sufficient friction for the clutch to grip and disengage properly. Not all fully synthetic engine oils conform to this JASO MA spec. Be aware. The JASO spec is more important than whether the oil is semi-synthetic or fully synthetic.
On my own bike, I am able to freewheel down the drive and engage first gear on the move, thus avoiding the 'clunk'. Then I stop at the bottom of the drive, still with clutch disengaged, rock the bike over to the right to (hopefully) splash some oil on the separated clutch plates, then set off normally. This is similar to Yaminator's suggestion of 24 Oct 2015. So far it is behaving well at 15000 miles, although I still intend stripping the clutch and oiling the plates at some time in the future, just to make the gearshift nicer and reduce shock loads on the gearsets during first gear engagement and gearchanges.
In my experience with mult-plate wet clutches, only the outer few plates do most of the disengagement/engagement. The inner plates are loathe to move and remain fairly static and hence are more prone to staying glued to the inside of the clutch basket. Periodic dismantling and oiling has to be the way forward.