Lack of concentration for sure,
Second though, crosswinds, they kill me. I can headwind and tailwind putt, but crosswinds get me all the time.
I'm the opposite! I can putt in crosswinds all day...cant stand to putt into head/tail.
I have my days where I just cant help but to tell myself that "I AM NOT GONNA MAKE THIS PUTT"...its brutal but it only happens occasionally and I dunno what causes it