mgt-login was working and returning user displayname and profile photo. However it is showing this error message in console.
This code worked as expected earlier.
<!DOCTYPE html>
<html>
<head>
<script src="https://unpkg.com/@microsoft/mgt/dist/bundle/mgt-loader.js"></script>
</head>
<body>
<title>Hello World</title>
<mgt-msal-provider client-id="[Client Id]"></mgt-msal-provider>
<mgt-login></mgt-login>
</body>
</html>
this is an issue that was recently introduced in 1.3 of the Microsoft Graph Toolkit. Good news is that the fix will be included in the next release (1.3.3) shortly. You can see this issue for more details: https://github.com/microsoftgraph/microsoft-graph-toolkit/issues/522