Stuck on boot

Output of the serial connection via GPIO (GND=Pin6, TX=Pin8, RX=Pin10):

Willkommen zu minicom 2.7.1

Optionen: I18n
Übersetzt am May 6 2018, 08:02:47.
Port /dev/ttyUSB0, 11:53:20

Drücken Sie CTRL-A Z für Hilfe zu speziellen Tasten
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bootloader version:211102-0b86f96

CTRL-A Z for help | 115200 8N1 | NOR | Minicom 2.7.1 | VT102 | Offline | ttyUSB0

Output of the serial connection via Debug Pins:

(C)SiFive
#help

Command list :
show
load
do
rb/rh/rl addr
wb/wh/wl addr val

CTRL-A Z for help | 9600 8N1 | NOR | Minicom 2.7.1 | VT102 | Offline | ttyUSB0

For the record: The support is very engaged but I had to return the boards as well. There seems to be no do-it-yourself solution for this issue, yet.