A while back the version of Lync I had installed on my Macbook started prompting to verify certificates and then wouldn’t connect to Office 365. I fiddled around a bit but couldn’t get it to work so I put it on the too hard pile for the time being.
Eventually got back to it and low and behold, once I apply this update:
That was recently released it all works as you can see above.
Now all we need is a OneDrive for Business Mac desktop sync app (which I don’t think is far away).