Hi Rahul,
Greetings from Syncfusion support,
We have validated your reported query.With the shared sample, the reported issue is due to missing style package reference in the _Host.cshtml. We have also modified the shared sample.
In addition with the shared code blocks, the for loop condition (for (int i = 0; i < Diagram.Connectors.Count; i++)) fails, hence it is skipped from calling the SfToast show method.
Also, we have internally resolved “SfToast doesn't hide until hovering the toast” with the SfToast, in the Nuget package version 18.3.53. With the shared sample you are using the version 18.3.52, which is the cause of the reported issue. Can you update the Nuget package to latest version, and check the reported issues from your end ?
Please get back to us if you face any difficulties,
Regards,
Indrajith