Engine Starts cold but hot times it gives a horrible shake

Starts perfectly cold but when hot at times when I start the engine gives a horrible shake and shudder and doesnt start. Occasionally losing the clutch.

Ive had the vehicle checked, had the clutch replaced, gearbox replaced and when I drive alot, stopping and starting as im a courier, after driving more than 100km when I start the vehicle the engine makes a shudder and shake and it doesnt start or the clutch goes to the floor not allowing me to put it or take it out of gear.

Ive had it checked by mechanics who didnt come across the problem when they test drove it and I had the clutch replaced and other parts and the problem still happens only when the vehicle is warmed up. Starting cold it starts perfectly. The gearbox was replaced no more than 3 months prior. My mechanics cant find the cause or a solution.