Lync for Mac 14.1.1 hanging when making calls (mostly)

I upgraded to Lync 4.1.1 about a month or two ago and now get regular (3-4 times a day) hangs. The hangs (spinning pinwheel of death) are mostly when trying to make a call (either through Lync EV or normal Lync calls), but not exclusively.

I have tried completely removing Lync and just re-installing the latest 14.1.1 version, but this did not seem to make any difference.

I have tried this with both Yosemite 10.10.5 and the El Capitan GM release and the results are the same.

Has anyone else seen this or have an idea how to fix it?

Thanks,

Paul