Error message on merging queries: We cannot convert a value of type Record to type List..

My suspicion is that this error must also be present somewhere in the query editor, at least I cannot think of any scenario in which this particular error would first show up when loading data.

Did you check all queries and all query steps?

Merging queries doesn't put records but tables in the new column. When this is expanded, then a code step is generated using function Table.ExpandTableColumn.

Your Column2 should be a table column (which is a list indeed, but not a separate list).

Maybe you can share your query code or some screen shots we can use for further investigation?