We have analyzed the stated issue. In 18.104.22.168h version, we have made some changes in Ajax request and the response format of FileExplorer. After updating to this/latest version, kindly ensure the Ajax request and response format in server side.
If you are using our build-in online hosted service, please make the following changes in ajaxAction API of the FileExplorer control.
If you have provided an individual service for handling Ajax request of “FileExplorer” control, please refer to the following document. This will be helpful to ensure changes in Ajax request and response format.
Document link: http://www.syncfusion.com/downloads/support/forum/120969/ze/Server_Side_operations_in_file_explorer_control331637042
Please try the sample and let us know whether it is enough or if you want File Explorer sample with local Web API service? If required, we will provide File Explorer sample with Web API service.
We have prepared a sample based on this and it can be downloaded from: http://www.syncfusion.com/downloads/support/forum/120969/ze/MVCAjaxHandling-453722444
If you still encounter this issue, please get back to us with more information like updated version, individual service or our build-in online service and code blocks of response. This would help us to investigate further and provide a solution to you.