Is it normal to have a grabby clutch on this bike? My friends Sherco 250 has the same as well.

Symptoms feel like you have given it too much clutch when moving slowly and the bike lurches forward. Also if the bike is left for a while the clutch is stuck quite solid and takes a bit of releasing - don't know if this is related.

Is there anything that can be done to improve it - tried an oil change with no improvement but was thinking a thicker oil may help say 20w 50

I use 15w50 with great success for the same problem and never had the clutch grab from a cold start unlike 10w30.

Never looked like slipping under big engine loads either. But my clutch is still in good nick.