I have already changed the USB ports but that makes no difference.
The stick also seems to be detected:
openhabian@openhab:~ $ lsusb
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 003: ID 1cf1:0030 Dresden Elektronik
Bus 001 Device 002: ID 2109:3431 VIA Labs, Inc. Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
I just plugged the stick into Windows 10 and it runs there.
Under Windows I have then also successfully flashed directly to version deCONZ_ConBeeII_0x26720700.bin.GCF.
But still no stick is detected under Linux and I can’t see any problem in the logs either:
-- Reboot --
Mar 14 22:21:48 openhab systemd[1]: Started deCONZ: ZigBee gateway -- REST API.
-- Subject: A start job for unit deconz.service has finished successfully
-- Defined-By: systemd
-- Support: https://www.debian.org/support
--
-- A start job for unit deconz.service has finished successfully.
--
-- The job identifier is 109.
Mar 14 22:21:49 openhab deCONZ[358]: QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '/tmp/runtime-openhabian'
Mar 14 22:21:50 openhab deCONZ[358]: libpng warning: iCCP: known incorrect sRGB profile
Mar 14 22:21:50 openhab deCONZ[358]: libpng warning: iCCP: known incorrect sRGB profile
Mar 14 22:21:51 openhab deCONZ[358]: This plugin does not support propagateSizeHints()
Mar 14 22:21:51 openhab deCONZ[358]: This plugin does not support propagateSizeHints()
That indicates that the stick is either removed from the PI or that it reboots. We often see this when theres not enough power. What Power supply do you use?
When using a Raspberry Pi, the original power supply is required to guarantee a stable gateway. Only this power supply delivers 5.1V and 2.5A (Raspberry Pi 3B+) respectively 3A (Raspberry Pi 4B). And it definitely has good quality.
Unfortunately, the orginal power supply did not bring success .
The stick is found on the Raspberry:
openhabian@openhab:~ $ lsusb
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 003: ID 1cf1:0030 Dresden Elektronik
Bus 001 Device 002: ID 2109:3431 VIA Labs, Inc. Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
openhabian@openhab:~ $ dmesg
[ 313.787442] usb 1-1.3: new full-speed USB device number 3 using xhci_hcd
[ 313.926485] usb 1-1.3: New USB device found, idVendor=1cf1, idProduct=0030, bcdDevice= 1.00
[ 313.926508] usb 1-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 313.926526] usb 1-1.3: Product: ConBee II
[ 313.926543] usb 1-1.3: Manufacturer: dresden elektronik ingenieurtechnik GmbH
[ 313.926560] usb 1-1.3: SerialNumber: DE2470694
[ 317.530053] usb 1-1.3: USB disconnect, device number 3
[ 317.827502] usb 1-1.3: new full-speed USB device number 4 using xhci_hcd
[ 317.966580] usb 1-1.3: New USB device found, idVendor=1cf1, idProduct=0030, bcdDevice= 1.00
[ 317.966602] usb 1-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 317.966621] usb 1-1.3: Product: ConBee II
[ 317.966638] usb 1-1.3: Manufacturer: dresden elektronik ingenieurtechnik GmbH
[ 317.966655] usb 1-1.3: SerialNumber: DE2470694
I would do a manually firmware rewrite with a Raspberry Pi and a separate SD card. Just write our Image with Desktop to the SD card for a temporary test system.
With this system it can be checked whether in the Phoscon App under Menu > Gateway > General > Firmware a version in the format 26xx0700 is available - and not “Firmware not connected”. If yes, a device can also be tried to be connected and controlled as a test.
.
) - access to the stick was possible again 
.