[SOLVED] Front fans don't always spin?

[Lajlaj]

I have a Fractal Design R5 case that has a slide on the front case where I can adjust the fan speed, if I put it at max, my front fans are spinning like they should. If I slide it to the left it stops making sound and they are still spinning and so on.
But when I start my PC while the slide being to the left, my front fans doesn't spin. They try to spin but stops every second... Is there something wrong, or is it normal for the front fans not to spin with the slide being set to lower speed?

This only happens when the slide is set to low speed, however if the slide is set to max speed the fans spin as they should wether before I startup my PC or not. I just find it weird that they do spin when I adjust the slide when my PC is on, but when I boot it with the slide being to the left it doesnt.

UPDATE: Fans started working again at low speed for some reason, no help needed

 

[Ralston18]

Well, for future reference there could be a dead spot (or two) on the slide.

Possibly some corrosion or dirt/debris that scrapped off after some use.

The slide is just a variable resistor and being generally mechanical and needing sure solid contact such problems are not unknown.