If the property pad is in the "layout section", and you select a constraint, it says "no layout properties". Why's that section even there, then? At the very least, it should switch to the Widget section automatically.
Looks like we covered that in this PR but it never merged. https://github.com/xamarin/md-addins/pull/648
Thanks so much for taking the time to submit this report! I can confirm using the latest Visual Studio 2017 for Mac Preview version 7.1 I am able to reproduce this issue. Marking this report as CONFIRMED.
The PR mentioned above still seems to be missing :-)