Please login to our demo site backend and review the configuration. Follow the below steps to review the configuration on our demo site.
1. Click "Administrator" under "Login As"
2. Copy the Username and Password into the inputs and login
3. Click "Community Builder" followed by "List Management" on the top menu bar
4. Edit "Grid layout" userlist
5. Click the "Column" tab
Review the column configuration carefully for it to display like shown below.
demo.cbdemosites.com/demos/community-builder/user-lists/grid-layout
If it's not working after doing so you've likely some sort of CSS conflict breaking the Bootstrap 4 grid CSS. Try switching to default Joomla protostar template, clearing Joomla cache, and refreshing the page to see if it then works.