I have the same thing happening, and here is my take on it. If im right or not, I dont know, but it seems logical to me.
I think I may be at least partically right, because I dont see the floaties all year long.
The filter will only filter out what gets passed through it. Depending on how long each day you run your pump, stuff which floats in may settle on the bottom of the pool. As the pump then comes on later, the stuff on the bottom gets disturbed and floats into the water column and becomes visible in front of the light at night. So, really, the cleaner the bottom is, the less of the floaties will be visible.
Durning winter I have lots of floaties too because I dont run my robot very much. During spring and summer, I run my robot a lot and filter longer and I dont see the floaties that I do in the winter time.