Creating a custom column that calculates the previous row value by previous hour, date, & store

Given your stated logic, and starting from the data in your second screenshot, the following code seems to do what you say you want:

Documentation is within the code and comments

let

//change next line to refer to your last table
    Source = Excel.CurrentWorkbook(){[Name="Table23"]}[Content],
    #"Changed Type" = Table.TransformColumnTypes(Source,{
        {"Store- Ke", Int64.Type}, {"Date", type date}, {"Order Create Hour (UTC)", type time}, 
        {"Total Consumed (w/o Cancellations)", Int64.Type}}),

//Group by Store-Ke and Date
// you can add a sort if necessary
//  then aggregate to create Orders Dropped column according to your state logic
    #"Grouped Rows" = Table.Group(#"Changed Type", {"Store- Ke", "Date"}, {
        {"Orders Dropped by Hour", (t)=>
            let 

            //To sequential rows, we add a column which is the same column shifted up one
            // the logic ensures that the first row in each subgroup will be set to the original value
            // and that no value can be less than zero (0)
                #"Shift Consume" = Table.FromColumns(
                    Table.ToColumns(t) &
                    {{null} & List.RemoveLastN(t[#"Total Consumed (w/o Cancellations)"],1)},
                    {"Store-Ke", "Date","Order Create Hour (UTC)","Total Consumed (w/o Cancellations)", "Shifted Consumed"}),
                #"Add Orders Dropped" = Table.AddColumn(
                    #"Shift Consume","Orders Dropped by Hour", each 
                        List.Max({0, 
                        ([#"Total Consumed (w/o Cancellations)"] - [Shifted Consumed]) ?? [#"Total Consumed (w/o Cancellations)"]}) ,
                         Int64.Type )
            in  
                #"Add Orders Dropped",
                type table[#"Order Create Hour (UTC)"=time, #"Total Consumed (w/o Cancellations)"=Int64.Type, 
                            Orders Dropped by Hour=Int64.Type]
                }
    }),
    #"Expanded Orders Dropped by Hour" = Table.ExpandTableColumn(#"Grouped Rows", "Orders Dropped by Hour", 
        {"Order Create Hour (UTC)", "Total Consumed (w/o Cancellations)", "Orders Dropped by Hour"})
in
    #"Expanded Orders Dropped by Hour"