Hi Jaro
Not a common problem. I assume it goes into gear fine, and it feels like it is fully engaged on the gear stick?
There are a few causes of this, but all internal to the gearbox so isn't an easy or quick fix. Does it pop out of gear when you accelerate, come off the throttle or just at a random time?
Did you purchase from a dealer? If so you should take it back and request that the issue is resolved.