this kinda happened to me because an enderman placed a block on the leaves that where supposed to prevent iron golems from spawning, try building in all three axis to prevent all golem spawning except in the kill chamber
I used to have this same problem, if you use geforce than there is a geforce panel that includes a vsync option but if you go to geforce experience there are also settings for it
FrogInALog
this kinda happened to me because an enderman placed a block on the leaves that where supposed to prevent iron golems from spawning, try building in all three axis to prevent all golem spawning except in the kill chamber