I have a Mazda BT-50 2013 it has a diesel engine, however I am having a starting issue whenever the engine gets hot.

Probably the most common cause of difficult hot-starting in a diesel engine is wear in the fuel pump. If the pump can’t generate the correct pressure due to wear, which is exacerbated by heat, then it may not generate the pressures required to operate the fuel injectors.

This particular engine has a fuel pump which has been known to wear and allow the fuel inside it to overheat, causing the vehicle to go into limp-home mode. But the engine (and many others like it from other brands which use common-rail injection technology) are also notorious for wearing out their fuel injectors over relatively low kilometres. Worn injectors could also be a cause of difficult hot starting.