Thanks for contacting Syncfusion support.
We are unable to reproduce the reported issue at our end. So we have prepared the sample for your reference and that can be download from the below link. In this sample we have called the Grid startEdit method within the contextMenuClick event to Edit the particular row. Still if you facing the same issue, please share the following details for further assistance,
1) Share the full Grid code example.
2) From your query, we found that you have used contextMenuClick and contextMenuOpen events. So please share that events code.
3) If you have used any additional or custom CSS, then share the CSS details.
4) If possible, try to reproduce the reported issue in the below attached sample and send back to us.
5) When you opened the Grid dialog template?.
6) Syncfucion package version.
Note: From your screenshot we found that you have selected multiple records before perform edit action. But currently Grid do not have the support for multiple row edit. So please select one row at time to perform the edit action.
Madhu Sudhanan P