This isn't a pressing issue but I'm curious about it since I submitted it as a bug on Engage (111846) and was told that it wouldn't be fixed. It seems like an important issue that would impact a number of users during development or testing. It took a while to figure it out when it first occurred for me.
If you have a site and you visit it using a url of http://localhost, you are unable to edit an ecom group, or create a new ecom group.
The issue is that some cookies aren't created. Cookies like TreeShopFilter aren't created. TreeShopFilter in particular is needed and since it's not there, the ShopID isn't created correctly.
I reproduced this in 8.6.1.6 and 8.6.1.7.
Create a copy of a site with a binding for 'localhost'. Visit as http://localhost/admin and log in.
Go to the Ecommerce section, right-click on a shop and click "Add Group". You'll receive an exception.
The obvious workaround is to use a different URL which isn't a problem. The real issue is knowing about that in the first place and figuring out why the ecom functionality doesn't work sometimes.