It is required to inspect your Project and Cloud Dialogflow to get further details. I have tried to look further for similar issues and it appears the responses [1][2] by third parties of the StackOverflow thread seems to be related to your issue.
In addition to that I have also found this third party article which also seems to be discussing the issue that you have encountered.
If still the issue is not resolved or If you have any technical queries or think your issue is related to code, you can post at the Stack Overflow or Server Fault and a community of developers will assist you.
In case there are any technical issues or you would like to request any feature you can report it at the Public Issues by selecting the right component here.
Please also note that Google Groups forum is meant for general discussion of the platform, not specific technical issues. You can find more info about Community Support Overview on Google Groups here.