@JimiT
I also tried various Capacitors with no effect. At least two methods were helpfull:
(1) use a short USB(A) - USB(C) cable (10 cm)
(2) remove the bottom plate while uploading (afterwards it runs with an 1m cable @921600 baud).

@jimit
I am using a direct USB-Connection to my Desktop-PC. A connection to my laptop has the same result.
But there is another problem I got when using the MP9250 example software and the "Playing MP3 from SD-Card" example:
Even when I'm just approaching to the M5stack (not touching) I often get several failures such as a reboot or a freeze. It doesn't depend wether the bottom is connected or not. I extra put a sheet of paper between my finger and the M5unit to be shure, there is no direct contact. I took a video of it, but is ist to big to upload it.
So I think my m5stack has a hardware problem. I'd like to test it with another M5stack but I have no other one and I dont want to buy one more because I don't know if there might be the same problem.

@jimit Hi Jimit,
I forgot to tell, that I am using the new 2018 model (with 9DOF-Sensor and USB-C). I have no Chance to press the Reset-Button in time , because there are only a few dots when "Connecting ..."at the beginning of upload. Also pressing the Reset-Button (before connecting) during the upload has no success.
But the Problem is not the start of the upload. Sometimes the upload continues up to 30 percent or 50 percent. Then there is a "timeout for waiting fot packet header".

But the upload is always ok, when I ...
(1) use a short USB-cable (I tried various 1m long cables at various USB ports (2.0 and 3.0), but no one performs)
(2) remove the Bottom-Plate (then a 1m cable is ok).

BTW Is there an example Code for the 9DOF-Sensor (new in 2018 model)?
BTW The "gift" wasn't in my development kit (does'nt matter, I have enough of them).

@JimiT
I also tried various Capacitors with no effect. At least two methods were helpfull:
(1) use a short USB(A) - USB(C) cable (10 cm)
(2) remove the bottom plate while uploading (afterwards it runs with an 1m cable @921600 baud).