My bike did exactly the same thing in a clubmans race, cracking along end of a long straight lockup in top nearly flat out jumped on the clutch. Freed up after but seized later that day again, freed up again after cooling but needs to be stripped down to see whats up before it grenades.

I did find that my water pump impeller was old and missing a blade - so potentially inline with overheating caused mine. Check the plastic water pump drive gear too they're prone to cracking and failing from what I saw of mine and a spare one. I've since replaced it but ive not had a thorough look at the top end - altho bike starts first kick i'm not going to run it properly until i've checked it out.

I was running premix Castrol TTS 35:1 standard carbs & airbox