Keywords for me :
a) new starter
b) when engine is hot

Thats a known Problem, because the aftermarket starter are not shielded well enough against heat. So the magnet Switch (Little device on top of the starter) is hanging.
It might as well be, because aftermarket Starters use a quickly evabporating
grease in the said Little starter device.

In any case, no Problem to start nayway, if you open up the Motor cover and use
a hammer to give that Little starter devive a notch with it.

It will engage imitiate and your Motor will start over.

Report back please