This is noted at Digital Publishing Suite Help | DPS Bug Fix Release Notes:
With a recent July hot fix, updating the DPS Desktop Tools results in the "v32" viewer version mistakenly appearing in the Viewer Version pop-up menu. When creating a folio or editing folio properties, do not select v32—v32 folios are not compatible with the current v31 viewer apps. Instead, select v31 or earlier. (We recommend using the default v26 setting.)
Neil