Remove initial zero values in a column

Here's one way to do it in the query editor with GroupKind.Local.  To see how it works, just create a blank query, open the Advanced Editor and replace the text there with the M code below.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMlDSUUpUitXBzjKEs4yArCQwyxjOMsDBSlaKjQUA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Column1 = _t, Column2 = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Column1", Int64.Type}}),
    #"Grouped Rows" = Table.Group(#"Changed Type", {"Column1"}, {{"AllRows", each _, type table}}, GroupKind.Local),
    #"Removed Top Rows" = Table.Skip(#"Grouped Rows",1),
    #"Expanded AllRows" = Table.ExpandTableColumn(#"Removed Top Rows", "AllRows", {"Column2"}, {"Column2"}),
    #"Changed Type1" = Table.TransformColumnTypes(#"Expanded AllRows",{{"Column2", type text}})
in
    #"Changed Type1"

Or, here is how to do it with List.PositionOf

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMlDSUUpUitUhxDICspLALGM4ywAHK1kpNhYA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Column1 = _t, Column2 = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Column1", Int64.Type}}),
    Custom1 = List.PositionOf(#"Changed Type"[Column1], 1, Occurrence.First, (x,y)=> if x<>0 then true else false),
    Custom2 = Table.Skip(#"Changed Type", Custom1)
in
    Custom2

If you try both and they both work, please report back which is more performant.

Pat