mrmiiike,
I wouldn’t call it is a sin, unless it either was an intential act of disrespect or an intentional disregard to do something that you knew was not proper. It is kind of like men wearing hats indoors, particularly in church. It is more common today for men to wear hats indoors today than it was decades ago. But one place men will be repremanded for wearing a hat indoors is in court. Regardless of how popular it might be at the country music awards or the Grammy’s, it is still not proper in court and the judge will let you know it. Is there something sinful about wearing a hat indoors? Not always, but it can be a sign of disrespect. And when you know something is considered disrespectful and you do it anyway, then it is wrong.
{I’m just not certain that all pastors have knowledge that it is wrong to ever clap in church.}