Power Query help please - Refresh error: "Please rebuild this data combination"

Hi, I have suddenly started getting this error:

I have read this blog: 

https://www.excelguru.ca/blog/2015/03/11/power-query-errors-please-rebuild-this-data-combination/

But this webpage states that the problem is caused by combining different data sources - I have only one data source which is a folder of excel files.

Here is my code:

let
    Source = Folder.Files("S:\Operations\Scheduled Reports\WH083_SLA"),
    #"Filtered Hidden Files1" = Table.SelectRows(Source, each [Attributes]?[Hidden]? <> true),
    #"Invoke Custom Function1" = Table.AddColumn(#"Filtered Hidden Files1", "Transform File", each #"Transform File"([Content])),
    #"Renamed Columns1" = Table.RenameColumns(#"Invoke Custom Function1", {"Name", "Source.Name"}),
    #"Removed Other Columns1" = Table.SelectColumns(#"Renamed Columns1", {"Source.Name", "Transform File"}),
    #"Expanded Table Column1" = Table.ExpandTableColumn(#"Removed Other Columns1", "Transform File", Table.ColumnNames(#"Transform File"(#"Sample File"))),
    #"Changed Type" = Table.TransformColumnTypes(#"Expanded Table Column1",{{"Source.Name", type text}, {"ATMSDelivReq.DelReqCode", type text}, {"ATMSDelivReq.CreatedDate", type date}, {"ATMSDelivReq.CreatedTime", type time}, {"ATMSDelivReq.EarliestDelivDate", type date}, {"ATMSDelivReq.LatestDelivDate", type date}, {"ATMSDelivReq.OrderType", type text}, {"ATMSDelivReq.RefLine1Class/Order", type text}, {"ATMSDelivReq.RefLine2OrderLine", Int64.Type}, {"ATMSDelivReq.ReqNumberOf", Int64.Type}, {"ATMSDelivReq.PickedSoFar", Int64.Type}, {"Allocated not picked", Int64.Type}, {"ATMSDelivReq.StockAllocSoFar", Int64.Type}, {"ATMSDelivReq.DespatchedSoFar", Int64.Type}}),
    #"Filtered Rows3" = Table.SelectRows(#"Changed Type", each not Text.StartsWith([ATMSCustomerGroup.NACode], "NA6198") or [ATMSCustomerGroup.NACode] <> "NA6199"),
    #"Removed Other Columns" = Table.SelectColumns(#"Filtered Rows3",{"Source.Name", "ATMSDelivReq.DelReqCode", "ATMSDelivReq.CreatedDate", "ATMSDelivReq.EarliestDelivDate", "ATMSDelivReq.LatestDelivDate", "ATMSDelivReq.ReqNumberOf", "ATMSDelivReq.StockAllocSoFar", "ATMSDelivReq.PickedSoFar", "ATMSDelivReq.DespatchedSoFar", "ATMSDelivReq.RefLine1Class/Order", "ATMSCustomerGroup.NACode", "ATMSDelivReq.RefLine2OrderLine", "Allocated not picked"}),
    #"Filtered Rows" = Table.SelectRows(#"Removed Other Columns", each Text.StartsWith([#"ATMSDelivReq.RefLine1Class/Order"], "SPRE") or Text.StartsWith([#"ATMSDelivReq.RefLine1Class/Order"], "SREC")),
    #"Extracted Text Range" = Table.TransformColumns(#"Filtered Rows", {{"Source.Name", each Text.Middle(_, 10, 8), type text}}),
    #"Changed Type1" = Table.TransformColumnTypes(#"Extracted Text Range",{{"Source.Name", type date}}),
    #"Renamed Columns" = Table.RenameColumns(#"Changed Type1",{{"Source.Name", "ReportDate"}, {"ATMSDelivReq.DelReqCode", "DelReqCode"}, {"ATMSDelivReq.CreatedDate", "CreatedDate"}, {"ATMSDelivReq.EarliestDelivDate", "EarliestDelivDate"}, {"ATMSDelivReq.LatestDelivDate", "LatestDelivDate"}, {"ATMSDelivReq.RefLine1Class/Order", "RefLine1Class/Order"}, {"ATMSDelivReq.ReqNumberOf", "ReqNumberOf"}, {"ATMSDelivReq.PickedSoFar", "PickedSoFar"}, {"ATMSDelivReq.StockAllocSoFar", "StockAllocSoFar"}, {"ATMSDelivReq.DespatchedSoFar", "DespatchedSoFar"}, {"ATMSDelivReq.RefLine2OrderLine", "RefLine2OrderLine"}, {"ATMSCustomerGroup.NACode", "NACode"}}),
    #"Removed Errors" = Table.RemoveRowsWithErrors(#"Renamed Columns", {"RefLine2OrderLine"}),
    #"Removed Duplicates" = Table.Distinct(#"Removed Errors", {"ReportDate", "DelReqCode"}),
    #"Inserted Text After Delimiter" = Table.AddColumn(#"Removed Duplicates", "Text After Delimiter", each Text.AfterDelimiter([#"RefLine1Class/Order"], "/"), type text),
    #"Renamed Columns2" = Table.RenameColumns(#"Inserted Text After Delimiter",{{"Text After Delimiter", "OrderNo"}, {"RefLine2OrderLine", "OrderLine"}}),
    #"Inserted Merged Column" = Table.AddColumn(#"Renamed Columns2", "Merged", each Text.Combine({[OrderNo], "-", Text.From([OrderLine], "en-GB")}), type text),
    #"Renamed Columns3" = Table.RenameColumns(#"Inserted Merged Column",{{"Merged", "OrderLine-ID"}}),
    #"Filtered Rows1" = Table.SelectRows(#"Renamed Columns3", each [LatestDelivDate] <> null and [LatestDelivDate] > #date(2023, 4, 4) ),
    #"Filtered Rows2" = Table.SelectRows(#"Filtered Rows1", each Duration.Days([LatestDelivDate]-[CreatedDate]) > 1)
in
    #"Filtered Rows2"

Thanks in advance!