Hi Ali,
Greetings from Syncfusion support.
We have confirmed it as a bug and logged the defect report
“Problem with selecting cells by dragging mouse pointer” for the same. Thank you for taking the time to report this issue and helping us improve our product. At Syncfusion, we are committed to fixing all validated defects
(subject to technological feasibility and Product Development Life Cycle) and including the defect fix in our upcoming Bi-weekly release which is expected to be rolled by the mid of September, 2020.
You can now track the current status of your request, review the proposed resolution timeline, and contact us for any further inquiries through this link.
Please get back to us if you need further assistance.
Regards,
Renjith Singh Rajendran