The clutch plates can "lock" together. The plates are oil coated, the oil causes a suction between the plates after sitting. Normally rocking the bike in gear with engine off will break the bond. I've had them "stick" so bad they would not free up rocking the bike. I've had to start bike, rev it up pretty high and "dump" the clutch. If you use this method of "dumping" the clutch, be careful, when the plates "break" free, bike will take off on you.
Before you do this, in neutral, can you push bike? Trying to eliminate the mid gear or final drive isn't the cause.