Suggests there's other variables involved, like time of day taken, other supplements taken simultaneously, metabolic processes, diet, and maybe even the placebo effect.

If you pubmed vitamin d and sleep you find that in general vitamin d makes sleep quality worse. (I'm sure there are exceptions)

I have a wealth of experiential data on this, validated as recently as this previous July over a two week period. Like clockwork, if I take my Vit D supplement in the evening (like before bed), I will have almost zero REM sleep and will wake up from 8 hours of sleep exhausted. I have no idea why this happens but it's very repeatable.