Not had this issue myself and I am on 88000. Just a suggestion but could it be an oil pressure problem? OK when cold and oil more viscous but warm oil is thinner so takes a few seconds to circulate to valve gear. After leaving for a while oil drains but still warm and thinner so takes a few seconds to circulate again. Might be worth exploring if there is a non-return oil valve, grade of oil used and oil filter? Other forum members are probably more knowledgeable than me.