The new implementation of batch create no longer amalgamates multiple input fields in single spreadsheet cell.
So for example, in previous implementation you would have Lines.Account which would contain Account field for all line items.
New implementation separates Lines.Account field into multiple - one per each line item.
So instead of Lines.Account, you use Lines.1.Account, Lines.2.Account etc. where number represents line number.
You can create test business, create test transaction and do batch update to see how the schema works now.