I have an imac (retina display) & two external displays. If I bring up mylio on the imac it is fine, but if I move it to one of the external displays, the font is huge. The font in the info window is fine though.
When I brought up mylio on the external display it is fine, then I move it to the retina display & the dashboard font shrinks to tiny.
It’s annoying, but not a big deal. I mention it so you will know it is happening, at least for me.