18.04 amd-64 usbguard-0.7.2 fresh install problem

1) Ubuntu package usbguard-0.7.2 installed via sudo apt-get install - SUCCESS
2) /etc/usbguard/rules.conf exists; still empty
3) sudo usbguard generate-policy > rules.conf unproductive until chmod o+w rules.conf, then again generate-policy ...
4) sudo more rules.conf - SUCCESS: rules for Linux usb drivers and for usb devices present are listed (class 09:*:*, 07:*:*, and 03:*:*)
5) sudo chmod o-w rules.conf
6) sudo systemctl restart usbguard.service
7) sudo systemctl enable usbguard.service
8) sudo systemctl status usbguard - SUCCESS: daemon is active
9) with the intent of now adding yet disconnected devices for usbguard allow-device -p <device id>, plug in USB stick
10) lsusb, then sudo lshw - SUCCESS: USB stick characteristics identified, but not yet mounted - not registered by lsblk or df -H
11)From lsusb output extract USB stick device id: 13fe:1d00
12) sudo usbguard allow-device -p 13fe:1d00 - ERROR
          usbguard-daemon[949]: IPC: client_pid=2705: IPC exception: Rule set upsert: Rule: Cannot upsert: multiple matching rules

Step 12) ends in similar outcome, regardless of file permission of rules.conf .
STUCK: in rules.conf no second/(or more) device(s) with id 13fe:1d00 or with interface {08:06:50} - so, what matches ?
Looking forward, what are my next steps ?
Thanks in advance for any hint !