We have experienced an issue where when someone shares both their screens, and give the party on the other end full control, it does not let the party on the other end to click on the second screen ( not the primary ) on the first attempt. When they click, it takes them back to the primary screen. On the second attempt, it lets them to click on the second screen. However, If they first click on the primary screen and then scroll to the second screen they do not encounter the issue.
We are running Windows 10 with Skype for Business client and Skype for Business 2016 server on our environment.