I’m going to document the current situation here:
Today I had a really hard time to get the laptop starting up at all. Usually it would just hang in the BIOS boot process. There was a short flickering of the screen, the Charge LED on the side would flash ~13 times green, then once orange and then again several time green. After this nothing would happen until I power down the system.
Two times the system managed to boot at all, but then for example Bluetooth would not work. The log showed
kernel: usb usb3-port7: attempt power cycle
kernel: usb usb3-port7: unable to enumerate USB device
kernel: usb usb3-port9: attempt power cycle
kernel: usb usb3-port9: unable to enumerate USB device
kernel: usb usb3-port10: attempt power cycle
kernel: usb usb3-port10: unable to enumerate USB device
kernel: usb usb3-port7: attempt power cycle
kernel: usb usb3-port7: unable to enumerate USB device
kernel: usb usb3-port9: attempt power cycle
kernel: usb usb3-port9: unable to enumerate USB device
kernel: usb usb3-port10: attempt power cycle
kernel: usb usb3-port10: unable to enumerate USB device
kernel: usb usb3-port7: attempt power cycle
kernel: usb usb3-port7: unable to enumerate USB device
kernel: usb usb3-port9: attempt power cycle
kernel: usb usb3-port9: unable to enumerate USB device
kernel: usb usb3-port10: attempt power cycle
kernel: usb usb3-port10: unable to enumerate USB device
So, I guessed it could be a USB problem. I detached all expansion cards. For now the laptop is working.
In my opinion I’m hitting a problem again, I had a while back. This was never properly resolved, I just switched to an external HDMI adapter.