Union appends records from incoming streams. It doesn't match keys or remove duplicate rows. Choose automatic configuration by field name when exports represent the same fields in different column orders. Amount should land under Amount even if one file places it first and another places it second. Inspect the resulting metadata and any warnings about missing or mixed fields.
Configuration by position ignores names and lines up the first column with the first column, then the second with the second. That is useful only when the source positions have an agreed meaning. A shifted export can otherwise put a team label into an amount column. Missing fields in a name-based union become null for the affected records. Make the alignment rule part of your report handoff, because a correct record count alone won't expose a column mismatch.