I have a similar issue with the one describe here, but couldn't see any solution. Microsoft Team Members are not in the associated SharePoint site Members group
Issue: When I add a member in Teams group, he appears as a member in the associated SharePoint site but it is not added to the default "Members group". So he cannot see any folder in SharePoint as he has not rights to do anything.
Question: Long story short, I believe the "Members group was deleted" by accident, and now I need to restore it. The members group to be restored should look like this (as default) I'm looking all over the internet, and can't seem to find a solution. Anyone out there who is a genius, appreciate your help.