Hi Taki,

After reviewing the configuration, we found that it combines server-side paging with client-side grouping. Because serverGrouping is not enabled, grouping is performed on the client by default. The default value of serverGrouping is false.

So the following configuration is contradictory: 

group: { field: "OrderDate" },
serverPaging: true,
// serverGrouping is not set, so it defaults to false 

OR when using wrappers:

 .DataSource(dataSource => dataSource      .
      .ServerFiltering(true)
      .ServerPaging(true)
      .ServerSorting(true)
      .Group(group => group.Add("Section", typeof(int)))
      ......
  )

This asks the server to own paging while the client owns grouping. The two cannot be satisfied together. Grouping requires knowing which group every record belongs to, but with serverPaging: true the client only ever holds one page. It cannot know how many groups exist, how many items each contains, or where each group starts and ends. Without that information the virtual list cannot calculate scroll geometry, so it does not request further pages. 

In addition, as mentioned in the documentation mixed data operations are not supported. All data operations have to occur either on the server or on the client. 

Why it appeared to work before

It did not actually work; it only looked like it did.

The previous renderer used a single flat list and treated grouping as decoration. It stamped a header whenever the group value changed between two adjacent items. Since the client only ever had one page, those headers described that page rather than the data set: the same group could reappear across pages, and group item counts were never known. Virtualization kept working only because the old renderer ignored grouping entirely when positioning items.

The current implementation renders each group as its own section with real, globally indexed boundaries. Correct grouping cannot be derived from a single page, so the component now requires  serverGrouping  rather than producing misleading headers. What changed is the removal of a cosmetic illusion, not of working functionality.

Working configuration

Virtualization combined with grouping is supported when grouping is done on the server. 

To use virtualization with grouping, please enable server grouping and ensure that your server endpoint supports grouping and returns the data in the format expected by the component.

With the above said, I am changing the status of the item to "Declined".

If you still encounter the problem, please share updated details and we will investigate it again.

I remain at your disposal in case you have any addiitonal questions on the matter.

Regards,
Neli
Progress Telerik