Need date differences by status change when status changes

Your updated example makes more sense, except for the missing Datediff entry on row 4 which I assume is a typo.  Try this:

let
    Source = Excel.CurrentWorkbook(){[Name="Table7"]}[Content],
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"ID", Int64.Type}, {"Status", Int64.Type}, {"Date", type date}}),

//Note use of GroupKind.Local
//Add a column showing the minimum date for each status group
    #"Grouped Rows" = Table.Group(#"Changed Type", {"ID", "Status"}, {
        {"all", (t)=> Table.AddColumn(t, "Min Date", each List.Min(t[Date])),     
        type table [ID=nullable number, Status=nullable number, Date=nullable date, Min Date = nullable date]}
        }, GroupKind.Local),

    #"Expanded all" = Table.ExpandTableColumn(#"Grouped Rows", "all", {"Date", "Min Date"}),

//Shift the min date column for easier comparisons
    #"Shifted Min Date" = Table.FromColumns(
        Table.ToColumns(#"Expanded all") &
        {{null} & List.RemoveLastN(#"Expanded all"[Min Date])},
        type table [ID=nullable number, Status=nullable number, Date=nullable date, Min Date = nullable date, Shifted Min = nullable date]
        ),

//Add the Datediff column at the change in status position
    #"Add Need"= Table.AddColumn(#"Shifted Min Date", "Datediff on Change", 
            each if Duration.Days([Min Date] - [Shifted Min])= 0 then null else Duration.Days([Min Date] - [Shifted Min]), Int64.Type),
    #"Removed Columns" = Table.RemoveColumns(#"Add Need",{"Shifted Min", "ID", "Min Date"})
in
    #"Removed Columns"