I asked a sheikh if my past prayer was valid he said it was not I delayed making it up due to laziness but intended to do it later I asked again and he said still invalid even if unintentional so I made it up is this a sin and does it count as kufr as Ibn Baz said about missing prayer

I believe you should have told the sheikh that you suffer from waswas so that he gets the full picture. Anyway, there is a saying that when somebody intentionally and without reason keeps delaying the salah, it is as if he abandoned salah altogether. Therefore, he doesn't have to make it up because this is considered disbelief. However, the other saying is that you do have to make them up.