[SOLVED] Weird 3-pin chassis fan connector

[Pupq1]

Hello, I've bought 2 3-pin Arctic F12s for my case and I plugged one into a 4 pin connector on my motherboard, and it worked, and the second fan I tried to plug into the other case fan connector on the motherboard, which is a 3 pin, but with an empty pin between one of the pins and the other 2, so like if you had a 4 pin connector and removed the second pin. I've tried to plug the fan in it in multiple ways (with only 2 pins going in cause you can't plug it any other way) and it doesn't work. I'm also pretty sure it is a case fan, since it says "Chassis" right next to it, but I don't know what it is, there is also no mention of the connector in the mobo manual. What kind of connector is it? Is there any way to make it work with my 3 pin fan?
My mb is an Asus Prime B250M-K

 

[CountMike]

Hello, I've bought 2 3-pin Arctic F12s for my case and I plugged one into a 4 pin connector on my motherboard, and it worked, and the second fan I tried to plug into the other case fan connector on the motherboard, which is a 3 pin, but with an empty pin between one of the pins and the other 2, so like if you had a 4 pin connector and removed the second pin. I've tried to plug the fan in it in multiple ways (with only 2 pins going in cause you can't plug it any other way) and it doesn't work. I'm also pretty sure it is a case fan, since it says "Chassis" right next to it, but I don't know what it is, there is also no mention of the connector in the mobo manual. What kind of connector is it? Is there any way to make it work with my 3 pin fan?
My mb is an Asus Prime B250M-K

That MB has only one chassis fan connector so that weird one is for something else, most probably Digital SPDIF sound connector. according to manual https://dlcdnets.asus.com/pub/ASUS/mb/LGA1151/Z170-K/E11133_MB_Pin_Definition_v2_web_only.pdf