Issue Summary

By default Org, admins should be site-admins to the sites linked with their Organizaiton.
If an Org admin is somehow removed from the site-admins group you can't give him the same access by changing his role.

Note that it shouldn't be possible to remove an Org admin from the site-admins group but there are some occasions where it happens like a site-import that re-creates the whole instance userbase.

Steps to Reproduce

1. Have an Org admin removed from the site-admins group
2. Try to change his role to Site administrator

Expected Results

The user role should be changed and he should be added to the site-admins group.

Actual Results

The change of role will fail and we can see the following error from the permisison endpoint that's called:

{"key":"badRequest","context":{"message":"Cannot remove an org admin from the site-admins group"}}

Workaround

Manually add the user back into the site-admins group.
If that doens't work, contact Atlassian Support.