When you first open the Spreadsheet editor and double-click a field that uses a suggestor widget, it works as expected, the suggestor appears in the field.
When you move to another cell, or even return to the same cell, the suggestor renders 1 line above the target field. If you edit a cell in the first row, the suggestor is totally hidden (I think by the header row).
Should be able to reproduce even just using Default domain in any Nuxeo installation:
-Edit result columns to add Subjects, for example.
-Open Spreadsheet editor.
-Double-click a Subjects cell to get the suggestor.
-Double-click another cell.