(example: 2.79b release)
(example: 2.80, edbf15d3c044, blender2.8, 2018-11-28, as found on the splash screen)
Short description of error
I've tried several different projects and intentionally put an object with a open section :
Then I keep trying shift+ctrl+alt+m as per the 2.8 Manual. Still it won't do anything. 2.79b, no problem works great. In 2.8 I don't see an error nor does it find any Non Manifolds. Also I did open the information window and no text was produced after hitting shift+ctrl+alt+m
Exact steps for others to reproduce the error
Based on the default startup or an attached .blend file (as simple as possible).