Hi Kamil
Greetings from Syncfusion support
Based on your query we found that the rows are undefined in the rowSelected event while using virtualization. We have prepared a sample by enabling the virtualization and select the rows using shift.
By default, while using virtualization only the rows rendered in the DOM element are included in the row object in args of the rowSelected event. It is the default behavior of EJ2 Grid. In your attached screenshot we found that you have all rows as undefined in your project, but we are unable to reproduce the mentioned issue in our sample.
Please refer the below Sample for your reference,
Please share the below details to validate the issue at our end and provide solution as soon as possible,
1. Share the issue reproduced sample or replicate the issue in the above sample
2. Share full grid code example
3. Syncfusion package version.
Regards
Vignesh Sivagnanam