OK, have moved this thread to the Mantis forum, now that model has been verified.
As far as the telemetry, what kind of file are you trying to upload? I don't have a Mantis, so I don't know how the telemetry is stored on that platform. Ideally, a zip file will upload the most reliably... but if uploading a different file format, try adding the .txt extension to the existing file name.
So if you are trying to upload the file log08012019.csv change the name to log08012019.csv.txt and then try to upload it.
OK, now regarding your lack of communication with the US Customer Service... even though this
is the 21st century, historically email has proven to be the least effective in contacting Yuneec CS, at least in the US.
I have tried to set up a phone conversation because you have to have an appointment but still get no response.
Just to clarify... so you setup a phone appointment and Yuneec CS did not call back at all?
I will say that in most cases, any contact with CS must be initiated by the customer. They simply do not call back (other than scheduled callbacks) or reply via email.
Also if this is a warranty claim, calling will not move you through their queue more quickly. However they usually are reasonable in the timeframe of replacement, should they rule in that direction. You simply may see a new Mantis on your doorstep... at least in your circumstances, you are dealing with only replacement.
Repairs add a whole additional layer of lack of communication and queue with a 3rd party authorized repair center... not to mention that company's inevitable supply chain issues with Yuneec, regarding parts availability.