I had a similar problem with a K series Caterham. Turned out the mounting face that the starter was bolted to wasn't true, so the starter was not perpendicular to the flywheel ring gear and moved enough off line when hot to jam up. Leave the car for a bit particularly with the bonnet off and it started fine. The starter was mounted right under the exhaust manifold. A new brize starter and fettling of the mounting face saw this problem sorted. Not sure if its relevant to your engine layout, but thought it worth a mention.

David
Aero S4