I always found Skype for Business/Lync got confused if you had the software installed but weren't part of the business' domain. My experiences with SfB were: 1.

I always found Skype for Business/Lync got confused if you had the software installed but weren't part of the business' domain. My experiences with SfB were: 1. I'm an outside contributor to a company using my personal machine. And 2. My organization but whilst using another organization's hardware. In both cases, joining Skype for Business meetings was downright nightmarish.