Hi people, how are you?

I'm new in the forum.. I recently bought a 2010 YFM700R almost new (5000km), and I have a particular issue.
When I start a ride, with the engine not in the optimal temperature, sometimes the gear jumps from 4th to 5th without touching the shift shaft.
It can be a clutch issue? or maybe something more complex in the transmission. When the engine is working in the optimal temperature, the transmission works fine.

thanks very much for your help.

Martin