Members cannot see Group Workspace

I created a Group Workspace within Power BI, and invited a few of my colleagues that haven't signed up to PowerBI yet.

They have subsequently signed up and have activated their Power BI pro trial, but were not able to see the Group Workspace that I have shared with them.

When I click on the Group Workspace > Edit Group, I can see the normal members with the "Member/Admin" drop down box, but for the people that signed up after I added them, that space is blank.

I also tried to use the bin icon to delete them from the group, and clicked save, but when I go back in, they are still in the group.

The only way I was able to add them to the workspace was to delete the whole group workspace, then publish the file again, and re-add them. However, I lose all my dashboards if I do that, so would like to avoid if possible.