It turns out that chip ID of USB-serial converter was a little different from the usual CH341:
Bus 001 Device 002: ID 1a86:7522 QinHeng Electronics USB Serial
so after manually loading ch341 module with:
sudo modprobe ch341
I had to enter also:
sudo sh -c "echo 1a86 7522 > /sys/bus/usb-serial/drivers/ch341-uart/new_id"
and now I have my device /dev/ttyUSB0
Hope this will be useful to someone else.
Regards,
Christian