User blog comment:DaNASCAT/Technical Update: October 21, 2015/@comment-5301469-20151023082022/@comment-126761-20151023093206

The normal undo/redo keyboard shortcuts should always work (although we are aware of an issue that can 'reset' these after previewing in the classic editor) - i.e. CTRL+Z and CTRL+Y. If there's somewhere these don't work, let us know!