2/3rds of the way down is when the bulk of the weight of the door is
on the opener. If your opener is chain drive and the chain is
stretched, that bounce can fool the opener into thinking it hit
something, so it reverses.

I've also seen openers themselves bounce at that point if they aren't
securely fastened to the ceiling.

To test your springs, unhook the door from the opener and open and
close it manually. If the springs are weak or need an adjustment, the
door will be VERY heavy at the 1/2-2/3rds mark.

Having said all that, take John's advice and contact the opener
manufacturer to see what they suggest.