Import JSON inside an Idea Workspace adds the document's columns and cards in a new row under everything already on the canvas, starting at its left edge. Each import used to be placed to the right of the one before, and after a few imports the cards were saved past the edge of the canvas, where they could not be seen.
The canvas grows to hold every card, so cards placed past its edge by earlier imports can be scrolled to. When an import finishes, a message says how many columns, cards and notes were added, and the view moves to the new cards. They are selected, so they can be dragged or deleted together.
When a pasted document is rejected, the message says that nothing was added, names the field that does not fit and lists the fields allowed in that place. Every JSON import box also reads a document followed by a sentence, as it already did for one preceded by a sentence or wrapped in a code block.