In a chart, you likely have Dimension(s) that limit the FIELDD and FIELDA to one value so your test would work. To use this expression as a filter, you will need to add an Aggr that specifies what Dimension(s) you are "doing over" this expression.
=Aggr( FIELDD='UnresolvedIntent' OR (FIELDA = 'Value' AND FIELDB = 'System' AND FIELDC='unresolved') , yourDImension)