Sort list view by Room

What type of field is this?

this field is relate field.

this field is relate field.

I dont know for sure but you could add 

'sortable' => false, to the list definition on the column. But i'm not sure if it will work since its a relate

I had this problem some time ago. I was told Relate fields are not sortable, there is an enhancement request which appears to be still open:

https://portal.sugarondemand.com/#supp_Bugs/58dfaecd-9633-8c68-809b-52d5f4a71600