The online forums seem to suggest that you need to speak clearly(I am sure you do) and slowly. They also suggest that you need to pause before and after reach command. The following is on the Google Voice Command help site.
//. Speak more slowly and clearly.
. Pause before and after each command. The text of your command might show in the document for a moment. For example, if you say "select all," the words "select all" show up before your text is selected.
. The microphone shows a bubble containing the most recent command. Verify that Docs or Slides heard the right command. If not, you can simply say "Undo."//
https://support.google.com/docs/answer/4492226?hl=en#zippy=%2Cadd-punctuation