I've added this constraint (based on your example) if(selected(${TreeFailureResult}, 'NONE') and count-selected(${TreeFailureResult}) > 1, false(), true() ) for my select_multiple but it doesn't trigger my constraint message "<b>None</b> can't be selected with other choices."?
I was also trying this approach (from an older GeoNet thread) to no effect: not(selected(., 'NONE') and (selected(.,'FIRE') or selected(.,'LOSL') or selected(.,'LOST') or selected(.,'OTHR') or selected(.,'PERS') or selected(.,'UTIL') or selected(.,'PROP') or selected(.,'PRUN') or selected(.,'REMV')))
I'm testing this in Survey123 Connect (not by publishing and using in the Survey123 App).