Power Query SUMIFS with Multiple Conditions

1. You will need to list only the columns that are needed to create a unique grouping, so probably NO.
2. For table type argument, you should list all of the columns that are in the "Grouped Table"
3. In that case, I would use a different approach.
   1. I don't know how you will access [Original Balance].
   2. In the code below, I arbitrarily set it to 2x the value of the first [Ending Balance] so the results would be the same.
   3. You will need to modify depending on how you have your "Period 1 Starting Balance"

let
    Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
    #"Changed Type" = Table.TransformColumnTypes(Source,{
        {"UID", type text}, {"Cost Code", type text}, {"Period", Int64.Type}, {"Ending Balance", Int64.Type}}),

//Index column to be able to restore processed results to original order
    #"Added Index" = Table.AddIndexColumn(#"Changed Type", "Index", 0, 1, Int64.Type),

//Group by UID and Cost Code
//  then compute the SUMIFS using a shifted column
// ASSUMES data sorted in Period order
    #"Grouped Rows" = Table.Group(#"Added Index", {"UID", "Cost Code"}, {
        {"Desired Result", (t)=>
            let
                #"Original Balance" = t{0}[Ending Balance] * 2, 
                #"Add Index2" = Table.AddIndexColumn(t,"Index2",0,1,Int64.Type),
                #"Add Results" = Table.AddColumn(#"Add Index2", "Desired Results", each 
                    if [Index2]=0 then #"Original Balance"-[Ending Balance]
                    else [Ending Balance] - #"Add Index2"{[Index2]-1}[Ending Balance], type number)
            in #"Add Results",
            type table[UID=text, Cost Code=text, Period=Int64.Type, Ending Balance=number, Index=Int64.Type, Index2=Int64.Type, Desired Results = number]}}),
    
    #"Expanded Desired Result" = Table.ExpandTableColumn(#"Grouped Rows", "Desired Result", {"Period", "Ending Balance", "Index", "Desired Results"}, {"Period", "Ending Balance", "Index", "Desired Results"}),
    #"Sorted Rows" = Table.Sort(#"Expanded Desired Result",{{"Index", Order.Ascending}}),
    #"Removed Columns" = Table.RemoveColumns(#"Sorted Rows",{"Index"})
in
    #"Removed Columns"