SPO ‘Check Permissions’ does not report SPO permission level for persons authorized via O365 Group; until that person visited the site for f
1. Modern Teams Site; permission mngt via O365 Groups
2. Authorize persons (e.g. batch via PowerShell) to the site, via adding as member to the O365 Group
3. Check access for person that should have access, as member of the Group; via 'Check Permissions'
4. This reports "None" for any accounts that have not visited the site yet.
Only for accounts that once visited the site (and are collected in 'SiteUsers' list; check permissions gives correct report-out.
Impact of the invalid report-out: 'check permissions' can not be trusted in case it reports 'None':
1. For person actually to have access; they may have access, but just did not use that yet.
2. More important: for persons that may not have access; the report-out of 'None' cannot be trusted => this person may have access via O365 Group, but just not (mis)use that access authorization yet.