a weak spot in stem

hello everyone ill try my best to describe my situation. plants are 2 weeks old in my top feed system and were looking great. but today i notest a week spot about 2 inches above the lava rock. best way i can describe it is picture the stem as a straw and the straw is being pinched but above and below this about a 1/4 inch pinch the stem looks great. the weak area is not black just looks a little mooshie. i belive i had to much water contacting this area. and right below the area in question i have little white bumps that looks like roots starting to form.
8 plants all affected, 2 have fell over.. i have moved the water flow away from the stem. question is am i going in the right direction, if not what can i do, do you belive they will come out of it. just any advise please. thanks a bunch

See if it looks like this- https://en.wikipedia.org/wiki/Damping_off

Stake up the plants that have fallen over; they may or may not make it. Move the water away from the stems as you have and try to be more mindful of their moisture levels at the stem base. This sort of thing happens from time to time. Good luck

thanks guys here is a picture. sorry for the quality best i can do.