Do the slight remnants of soap invalidate ghusl, and does the softness remaining in the hair or on the hand after washing indicate that the soap or conditioner has not been removed?

The cure for waswas (obsessive thoughts) is to ignore them. The fluid that exits does not necessitate ghusl (ritual bath) unless you are certain it is mani (semen), and its trace must be washed from clothing. You are not required to repeat ghusl if you find soap residue after performing ghusl with the intention of purification from janabah (major ritual impurity); the soap is removed with water even if a long time has passed. If the conditioner has a substance that prevents water from reaching the skin, it must be removed; otherwise, it has no effect.