Thanks for using Syncfusion products.
We checked AllowSort property and it is working fine as expected, please check in the following sample link. Ensure that you have not handled AllowSort property in TableControlQueryAllowSortColumn event. Also ensure that you have not added the column in the SortedColumns property.
Please let us know if this help and revert us if you need any further assistance on this.
Regards,
Arulraj A