Sorry, I do not have enough time for a detailed answer, i already go to 4.16, in short:
Just create a HISM (in blueprint editor!), add a simple cube mesh in the editor details panel and create a several Instances also in editor details panel. Then move the HISM in editor and that’s it.
This issue will be fixed for 4.17.2
Navigation with HISM instances also seems to be broken since 4.17. I’d assume that this is a related issue. See Navigation randomly skips HISM instances - AI - Unreal Engine Forums for a minimal project. Will this also be fixed in 4.17.2, as this prevents switching to 4.17?