Data refresh through PBI Gateway keep prompting credential missing incorrectly

Alright, I had a second session with the Microsoft Engineer and he said that there is some issue with folder data source.  We performed a test on our files:

1. Picked a Power BI report which was failing.
2. Replaced the folder data source to single *.csv or *.txt or *.xlsx (Engineer said this is just a workaround for now to temporarily fix our problem, please note this is not ideal when you have 100's of files you need to pick up from a folder e.g Daily Uber trip files).
3. Once I changed the folder to single *.csv or *.txt or *.xlsx source and upload on the server the refresh started working properly.
4. Now this is not an ideal solution for us, out of the 4 Power BI report which were failing I changed 2 of them to non folder data source and fixed it for the time being the remaining 2 are still a problem.

Microsoft Engineer did mention that they are aware of this issue and working on it right now.  Apparently they have 3 teams working on issue, Desktop Team, Gateway Team, Service Team.  Once they figure out where the problem is then they start working on the fix.

I will keep you guys posted on this issue once I get further info.  I am not sure if you have same issue as mine as other users in this community has SQL and other data source, but for my issues the Engineer knew that folder source is creating the problem.