Thank you for your interest in Syncfusion products.
I have checked the reported query in our end and I am unable to reproduce the issue in our end. Quartile formula is working properly in our end for all quart. So we requested you to please provide the sample which is reproduce the issue in your end. So that I can able to reproduce the issue in our end and we will provide required solution for you. Please refer the below sample and image which is used to reproduce the issue in our end.
Please let me know if you have any concerns.