Hi Max,
Thanks for contacting Syncfusion support.
We have checked your query and we didn’t faced those kind of issue in our side in WinRt. We have prepared a sample based on provided details and we are not able to reproduce the issue in our side.
Also, you have written some HeaderStyle, CellStyle and Converter for DateTimeColumn for SfDataGrid and we suspect, it may be cause of the issue. So, please modified the sample as per your replication scenario and revert us. It will be more helpful to provide better support.
Also, we recommended you to upgrade your WinRt version, it may resolve the issue in your side.
Regards,
Srinivasan