Repro steps:
- go to the RadClientDataSource binding demo: https://demos.telerik.com/aspnet-ajax/grid/examples/data-binding/client-side/client-data-source-binding/defaultcs.aspx
- filter a column so there is no data in the grid
- remove the filter
Actual: the pager is gone
Expected: the pager is there

SOLUTION: see the following KB article: https://www.telerik.com/support/kb/aspnet-ajax/grid/details/clientdatasource-binding-after-filtering-so-no-records-are-present-and-removing-the-filter-there-is-no-pager
You can show the pager when the filter command is executed:

function OnCommand(sender, args) {
    if (args.get_commandName() == "Filter") {
        $telerik.$(sender.get_element()).find(".rgPager").show();
    }
}

A fix in the codebase of the grid will take time, effort and will have to wait in the queue, which is why this is the official solution.