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?
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.