When I build a MASH network using aiStandins, they do not show in the viewport when it is set to Viewport 2.0. However, they do show in Legacy Default Viewport. I am using Maya 2017 update 4, but I have seen tutorials using Maya 2018 where they do show in the viewport -- is this simply a bug in Maya 2017? Any setting I can change to make them show?
What version of MtoA are you using?
This seems to be a fix that was put in place for Maya 2018, if you see the below release notes it says:
http://help.autodesk.com/view/MAYAUL/2018/ENU/?guid=GUID-86BDB101-2547-4E8B-9824-597EE20E4826
Activate your Legacy Viewport if you have problems with the instances in your viewports:
Try unhiding the original aiStandin (that was hidden when you create a Mash network), popped back up for me, seems like a viewport bug.