With Shampoos like Nizoral I usually have to "scrub" it reasonably hard... at least harder than my other shampoos, so dropping more hairs in the showers because of Noziral is not something I see as unusual. It helped my cause very well, no itch anymore, but I've since then moved on to regenepure DR because it's lighter on the keto but also has some other good stuff in it to keep your hair that you have left healthy and reasonably smooth.
Another proof of this is when I use conditioner after shampooing... even after having rinsed out a lot of the dropped hair (that got left stuck in there throughout the day) with the shampoo I still probably drop more hairs when using conditioner because it's thicker and is probably more likely to get hair glued to your hands than a shampoo that is more "watery".