webDoNotAggregate property
On some mobile web browsers, notably Chrome on Android, the speech results behave differently. The default behaviour is to aggregate separate phrases into a single result and return it. On Chrome Android that approach creates duplicates so this option can be used to disable the aggregation and return just the expected result. You will need to test the user agent of the browser to decide whether to use this option.
Implementation
static final SpeechConfigOption webDoNotAggregate =
SpeechConfigOption('web', 'aggregate', false);