i'd' give it time, i don't see anything alarming in diary. Early leaves aren't the prettiest.
is it a pale spot? what kind of 600w led? 600w from wall? 20" is likely too close and if that paly spot expands and you answered yes to any of that, then you need to move light further away. strips or quantum boards would be different and likely okay at that height, but no need to provide that much, yet.
plus, your top 4 leaves look to be growing from the same spot, as if there's no internodal space. Another sign it's too close.
It may take a few days before it starts growing again, if this is the case..