If the Sankey chart isn't loading the chart or the chart is blank you likely need to turn on the Lightning Web Security.
Go to Setup
Search for Session Settings
Under the section Lightning Web Security section of the page
Check Use Lightning Web Security for Lightning web components
You may also need to make sure the relationship records are being sent over to Salesforce during the sync process and that the usernames match the mailboxes in SigParser.
Salesforce should automatically turn this on after Jan 2023.