After some more days of testing and changing cables/position/usb ports the random disconnects still happen. This is what it looks like:
[Fr Jul 16 18:23:39 2021] usb 1-3.1: USB disconnect, device number 10
[Fr Jul 16 18:23:39 2021] usb 1-3.1: new full-speed USB device number 11 using xhci_hcd
[Fr Jul 16 18:23:39 2021] usb 1-3.1: New USB device found, idVendor=1cf1, idProduct=0030, bcdDevice= 1.00
[Fr Jul 16 18:23:39 2021] usb 1-3.1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[Fr Jul 16 18:23:39 2021] usb 1-3.1: Product: ConBee II
[Fr Jul 16 18:23:39 2021] usb 1-3.1: Manufacturer: dresden elektronik ingenieurtechnik GmbH
[Fr Jul 16 18:23:39 2021] usb 1-3.1: SerialNumber: DE2251106
[Fr Jul 16 18:23:39 2021] cdc_acm 1-3.1:1.0: ttyACM0: USB ACM device
[Fr Jul 16 18:23:43 2021] usb 1-3.1: USB disconnect, device number 11
[Fr Jul 16 18:23:43 2021] usb 1-3.1: new full-speed USB device number 12 using xhci_hcd
[Fr Jul 16 18:23:43 2021] usb 1-3.1: New USB device found, idVendor=1cf1, idProduct=0030, bcdDevice= 1.00
[Fr Jul 16 18:23:43 2021] usb 1-3.1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[Fr Jul 16 18:23:43 2021] usb 1-3.1: Product: ConBee II
[Fr Jul 16 18:23:43 2021] usb 1-3.1: Manufacturer: dresden elektronik ingenieurtechnik GmbH
[Fr Jul 16 18:23:43 2021] usb 1-3.1: SerialNumber: DE2251106
[Fr Jul 16 18:23:43 2021] cdc_acm 1-3.1:1.0: ttyACM0: USB ACM device
As you can see, 2 disconnects in a row, everytime this happens.
And here is the deCONZ Log from 18:23, if you need more, please ask!