Hi Muhammad Afiq,
Thank you for contacting Syncfusion support.
We have checked your reported issue with QueryBuilder in our latest version and the sample is working fine in our end. Please refer the below live demo and local sample.
And, we would like to let you know that the EJ2 QueryBuilder is available from the version (v16.4.42) so could you please ensure that the assembly references are loaded from latest version (i.e >16.4.42) in both local and runtime (using Output window from VS)? Since, we suspect that the cause of this issue is due to you have referred the Essential Studio product version less than (16.4.42).
For further details, please find our release notes and help doc links below.
Release Notes Link:
Help Doc Link:
Could you please check the above information and get back to us if you need any further assistance on this?