Google Assistant triggers "Default Fallback Intent" while Dialogflow does not - actions-on-google

Question

I created a chatbot which contains only one additional intent (depr_intent) along with the Default Welcome Intent and the Default Fallback Intent. This intent includes only the following training phrase: "What causes a person to get depressed and how can this be treated?". I set the ML CLASSIFICATION THRESHOLD to 0.2 .
When I enter on Dialogflow "I am a depressed person" then the depr_intent is triggered and the json response from Dialogflow is the following:
{
"id": "*****************************",
"timestamp": "2018-04-17T12:41:07.662Z",
"lang": "en",
"result": {
"source": "agent",
"resolvedQuery": "I am a depressed person",
"action": "5",
"actionIncomplete": false,
"parameters": {},
"contexts": [],
"metadata": {
"intentId": "*****************************",
"webhookUsed": "true",
"webhookForSlotFillingUsed": "false",
"webhookResponseTime": 253,
"intentName": "depr_intent"
},
"fulfillment": {
"speech": "...",
"source": "agent",
"displayText": "...",
"messages": [
{
"type": 0,
"speech": "..."
}
]
},
"score": 0.25
},
"status": {
"code": 200,
"errorType": "success",
"webhookTimedOut": false
},
"sessionId": "****************************"
}
Notice at the json response above that the score of this question is 0.25 .However, when I am entering the exact same phrase ("I am a depressed person") on Google Assistant (after entering "Talk to my test app" and getting triggered the Default Welcome Intent) then the Default Fallback Intent is triggered which responds "Sorry I did not find anything relevant to your question" and not the depr_intent. The DEBUG section on Google Assistant contains the following:
{
"response": "Sorry I did not find anything relevant to your question.",
"expectUserResponse": 1,
"conversationToken": "CiZDIzVhZD...",
"audioResponse": "//NExAARsA...",
"debugInfo": {
"assistantToAgentDebug": {
"curlCommand": "curl -v 'https://api.api.ai/api/integrations/google?token=*************************' -H 'Content-Type: application/json;charset=UTF-8' -H 'Google-Actions-API-Version: 2' -H 'Authorization: [token]' -A 'Mozilla/5.0 (compatible; Google-Cloud-Functions/2.1; +http://www.google.com/bot.html)' -X POST -d '{\"user\":{\"userId\":\"*************************\",\"locale\":\"en-US\",\"lastSeen\":\"2018-04-17T12:46:56Z\"},\"conversation\":{\"conversationId\":\"1523969239924\",\"type\":\"ACTIVE\",\"conversationToken\":\"[]\"},\"inputs\":[{\"intent\":\"actions.intent.TEXT\",\"rawInputs\":[{\"inputType\":\"KEYBOARD\",\"query\":\"I am a depressed person\"}],\"arguments\":[{\"name\":\"text\",\"rawText\":\"I am a depressed person\",\"textValue\":\"I am a depressed person\"}]}],\"surface\":{\"capabilities\":[{\"name\":\"actions.capability.SCREEN_OUTPUT\"},{\"name\":\"actions.capability.AUDIO_OUTPUT\"},{\"name\":\"actions.capability.WEB_BROWSER\"},{\"name\":\"actions.capability.MEDIA_RESPONSE_AUDIO\"}]},\"isInSandbox\":true,\"availableSurfaces\":[{\"capabilities\":[{\"name\":\"actions.capability.SCREEN_OUTPUT\"},{\"name\":\"actions.capability.AUDIO_OUTPUT\"}]}]}'",
"assistantToAgentJson": "{\"user\":{\"userId\":\"A****************************\",\"locale\":\"en-US\",\"lastSeen\":\"2018-04-17T12:46:56Z\"},\"conversation\":{\"conversationId\":\"1523969239924\",\"type\":\"ACTIVE\",\"conversationToken\":\"[]\"},\"inputs\":[{\"intent\":\"actions.intent.TEXT\",\"rawInputs\":[{\"inputType\":\"KEYBOARD\",\"query\":\"I am a depressed person\"}],\"arguments\":[{\"name\":\"text\",\"rawText\":\"I am a depressed person\",\"textValue\":\"I am a depressed person\"}]}],\"surface\":{\"capabilities\":[{\"name\":\"actions.capability.SCREEN_OUTPUT\"},{\"name\":\"actions.capability.AUDIO_OUTPUT\"},{\"name\":\"actions.capability.WEB_BROWSER\"},{\"name\":\"actions.capability.MEDIA_RESPONSE_AUDIO\"}]},\"isInSandbox\":true,\"availableSurfaces\":[{\"capabilities\":[{\"name\":\"actions.capability.SCREEN_OUTPUT\"},{\"name\":\"actions.capability.AUDIO_OUTPUT\"}]}]}"
},
"agentToAssistantDebug": {
"agentToAssistantJson": "{\"conversationToken\":\"[]\",\"expectUserResponse\":true,\"expectedInputs\":[{\"inputPrompt\":{\"richInitialPrompt\":{\"items\":[{\"simpleResponse\":{\"textToSpeech\":\"Sorry I did not find anything relevant to your question.\"}}]}},\"possibleIntents\":[{\"intent\":\"assistant.intent.action.TEXT\"}],\"speechBiasingHints\":[\"$Employee_names_MP\",\"$Employee_names_JT\",\"$Greeting_type\",\"$Objective_whoswho\",\"$Locations\"]}],\"responseMetadata\":{\"status\":{\"message\":\"Success (200)\"},\"queryMatchInfo\":{}}}"
},
"sharedDebugInfoList": []
},
"visualResponse": {
"visualElementsList": [
{
"displayText": {
"content": "Sorry I did not find anything relevant to your question."
}
}
],
"suggestionsList": [],
"agentLogoUrl": "https://www.gstatic.com/voice/opa/partner_icons/generic_3p_avatar.png"
},
"clientError": 0,
"is3pResponse": 1
}
Why is this happening?
Actually, even if I set the ML CLASSIFICATION THRESHOLD to 0.05 the same thing is happening on Google Assistant. Moreover, keep in mind that if I enter on Google Assistant "what causes a person to get depressed" then depr_intent is triggered (and apparently the same applies on Dialogflow). Finally, note that the fact that I am using a webhook at this basic bot does not make a difference (I think) since the same intents are triggered even without the webhook.
**
UPDATE
**
When I enter on Google Assistant "Why am I a person depressed" which has a score of 0.2800000011920929 (remember the ML CLASSIFICATION THRESHOLD is 0.2) then depr_intent is triggered. Personally, I am inclined to believe that Google Assistant has a minimum ML CLASSIFICATION THRESHOLD of 0.25. However, I entered two different phrases which each had score 0.25 and Google Assistant triggered depr_intent at the one and Default Fallback Intent at the other of them (while both triggered depr_intent on Dialogflow). Hence, I do not really know what is happening. But if we accept that probably there is a 0.25 minimum ML CLASSIFICATION THRESHOLD on Google Assistant then it may be that the former phrase was a bit above 0.25 and the latter one was a bit below 0.25 .