Here's a snippet of the block class to show my usage of the selection query:

public class StaffMemberBlock : BlockData {
    [Display(Name = "Staff Search", GroupName = SystemTabNames.Content, Order = 10)]
    [AutoSuggestSelection(typeof(StaffMemberSelectionQuery))]
    public virtual string Id { get; set; }
}

Hi Matthew,

Are you able to give an example of the Id string value?

The value is fetched via a GET request to the SelectionQueryStore (/episerver/Shell/stores/selectionquery), can you take a look at what response you're getting from that (your request will look something like: /episerver/Shell/stores/selectionquery/StaffMemberSelectionQuery/123)? Using some unsafe URL characters in the LineItem value can ultimately screw this up and might cause the behaviour you're seeing.

Found the issue! A rewrite rule in my web config was adding a trailing slash, which that store does handle as I expected.

I checked the network requests from the web inspector and found this GET for /EPiServer/Shell/stores/selectionquery/PublicWebsite.Models.SelectionQueries.StaffMemberSelectionQuery/brian-m-wicklund/ which returns

{}&&{"name":"","id":""}

After removing the rule the request became /EPiServer/Shell/stores/selectionquery/PublicWebsite.Models.SelectionQueries.StaffMemberSelectionQuery/brian-m-wicklund which returns

{}&&{"name":"Wicklund, Brian M.","id":"brian-m-wicklund"}