I'm just curious , I was in a SoO normal pug group , we cleared 4 bosses and everything was alright.
Then the leader decided to kick me for no reason , and he also ignored me.
Just my luck with people?
Hard to say, since it's unlikely any of us were there and you haven't provided much in the way of details.
I suspect there probably was a reason, and you either aren't telling us what it is because it might reflect poorly on you, or there was a reason and you honestly have no idea what it was.
Those two options just seem more likely to me than a group leader just randomly kicking you for no reason.
I've never encountered that before, no. There could be a lot of reasons for that behavior.
You could have been under-performing or standing in shit or annoying them, he could have been waiting to get someone in on Galakras who had been saved, a friend or guildied could have logged on... but, regardless of his reason, not saying anything and just kicking you is a pretty assholeish thing to do.