Resolume interface fps will change to match the output monitor refresh rate. However, if you had vsync turned on and your GPU could only render the output at less than 60fps, it could drop it down to 30fps to keep locked with vsync.
I would not expect this with a GTX 1080, but I guess it could happen if you wernt using DXV or there was some other reason it couldnt keep up or its not actually using the GTX 1080.