Concatenated columns differ

The two inputs of a Concatenate node have different columns. The node still stacks the rows and matches columns by name, but a column found on only one side is empty for the rows from the other, so later steps may see gaps.

What to do

If both inputs should have the same columns, rename columns in an earlier step or in the source files so the names match. If the difference is intended, no action is needed. The message lists the columns found on only one side.

Where it comes from

Shown by Concatenate. It is one of the messages about a node.