Communication problem Arduino Mega 2560 - PC

we have a project where we use an Arduino Mega 2560 for datalogging. The
arduino sends
periodically (2s cycle) a string containing different sensor values.

Our problem is that logview hangs up from time to time. The serial
logging stops can't open the COM-Port anymore but the UART from the Atmega2560 to the Atmerga16U2 is still sending.
The only solution is to unplug and reconnect the USB-cable. Unfortunately, this isn't an acceptable solution for us.

What we have tried so far:

  • We removed all sensors/actors from the Arduino Mega 2560 and sent only
    dummy strings over USB -> log still hangs up
  • We reduced the baudrate --> still hangs up
  • We used shorter USB-cables --> still hangs up
  • We used on the PC a simple PC-program writing serial data to a file
    (instead of logview) --> also hangs up
  • We connected an additional arduino USART/USB converter to the second
    USART from the Arduino and sent the same strings over both UARTS. On PC
    we watched both ports with logview and putty -> both hanged up
  • We tested this also with different PC's.
    Our OS Debian.

You have any idea? We think that it could be

  • problem with ground

Best regards