Howto prevent UDEV wrongly enqueues remove event for device ppp?

Connecting a PDA device with Debian Buster using SynCE, USB serial device is recognized and connects with ttyUSB bus, obtains an IP address and disconnects after a few seconds (two, max three). This is how it looks in syslog: Jan 18 20:26:57 debian10 dccm: Message: synce_device_dbus_init: registering object path '/org/synce/dccm/Device/_devices_pci0000_00_0000_00_06_0_usb2_2_2_2_2_1_0_ttyUSB0_tty_ttyUSB0' Jan 18 20:26:57 debian10 dccm: DEBUG: synce_device_manager_device_obj_path_changed_cb: sending connected signal for /org/synce/dccm/Device/_devices_pci0000_00_0000_00_06_0_usb2_2_2_2_2_1_0_ttyUSB0_tty_ttyUSB0 Jan 18 20:26:57 debian10 dccm: DEBUG: synce_device_dbus_init: obj_path set to /org/synce/dccm/Device/_devices_pci0000_00_0000_00_06_0_usb2_2_2_2_2_1_0_ttyUSB0_tty_ttyUSB0 Jan 18 20:26:57 debian10 dccm: DEBUG: get_password_flag_text: setting password flags unset Jan 18 20:26:57 debian10 dccm: DEBUG: synce_device_legacy_info_received: setting CTRL_STATE_CONNECTED Jan 18 20:26:58 debian10 dccm: DEBUG: gudev_uevent_callback: received uevent **remove** for device /sys/devices/virtual/net/ppp0/queues/tx-0 Jan 18 20:26:58 debian10 dccm: DEBUG: gudev_uevent_callback: received uevent **remove** for device /sys/devices/virtual/net/ppp0/queues/rx-0 Jan 18 20:26:58 debian10 dccm: DEBUG: gudev_uevent_callback: received uevent **remove** for device /sys/devices/virtual/net/ppp0 Seeing the output, I decided to delve deeper into monitoring UDEV events with "udevadm control -l debug"... and this was the result: Jan 23 15:01:28 debian10 dccm: DEBUG: get_password_flag_text: setting password flags unset Jan 23 15:01:30 debian10 systemd-udevd: Cleanup idle workers Jan 23 15:01:30 debian10 systemd-udevd: Unload module index Jan 23 15:01:30 debian10 systemd-udevd: Unloaded link configuration context. Jan 23 15:01:30 debian10 systemd-udevd: Unload module index Jan 23 15:01:30 debian10 systemd-udevd: Unloaded link configuration context. Jan 23 15:01:30 debian10 systemd-udevd: Worker exited Jan 23 15:01:30 debian10 systemd-udevd: Worker exited Jan 23 15:01:30 debian10 systemd-udevd: rx-0: Device (SEQNUM=1738, ACTION=remove) is queued Jan 23 15:01:30 debian10 systemd-udevd: Validate module index Jan 23 15:01:30 debian10 systemd-udevd: Check if link configuration needs reloading. Jan 23 15:01:30 debian10 systemd-udevd: Successfully forked off 'n/a' as PID 1327. Jan 23 15:01:30 debian10 systemd-udevd: rx-0: Worker is forked for processing SEQNUM=1738. Jan 23 15:01:30 debian10 systemd-udevd: tx-0: Device (SEQNUM=1739, ACTION=remove) is queued Jan 23 15:01:30 debian10 systemd-udevd: Successfully forked off 'n/a' as PID 1328. Jan 23 15:01:30 debian10 systemd-udevd: tx-0: Worker is forked for processing SEQNUM=1739. Jan 23 15:01:30 debian10 systemd-udevd: ppp0: Device (SEQNUM=1740, ACTION=remove) is queued Jan 23 15:01:30 debian10 systemd-udevd: rx-0: Processing device (SEQNUM=1738, ACTION=remove) Jan 23 15:01:30 debian10 systemd-udevd: tx-0: Processing device (SEQNUM=1739, ACTION=remove) Jan 23 15:01:30 debian10 dccm: DEBUG: gudev_uevent_callback: received uevent remove for device /sys/devices/virtual/net/ppp0/queues/tx-0 Jan 23 15:01:30 debian10 systemd-udevd: tx-0: Device (SEQNUM=1739, ACTION=remove) processed Jan 23 15:01:30 debian10 dccm: DEBUG: gudev_uevent_callback: received uevent remove for device /sys/devices/virtual/net/ppp0/queues/rx-0 Jan 23 15:01:30 debian10 systemd-udevd: rx-0: Device (SEQNUM=1738, ACTION=remove) processed Jan 23 15:01:30 debian10 systemd-udevd: rx-0: sd-device-monitor: Passed 157 byte to netlink monitor Jan 23 15:01:30 debian10 systemd-udevd: tx-0: sd-device-monitor: Passed 157 byte to netlink monitor Jan 23 15:01:30 debian10 systemd-udevd: ppp0: sd-device-monitor: Passed 179 byte to netlink monitor Jan 23 15:01:30 debian10 systemd-udevd: ppp0: Processing device (SEQNUM=1740, ACTION=remove) Jan 23 15:01:30 debian10 systemd-udevd: ppp0: RUN 'ifupdown-hotplug' /usr/lib/udev/rules.d/80-ifupdown.rules:5 Jan 23 15:01:30 debian10 systemd-udevd: ppp0: IMPORT builtin 'path_id' /usr/lib/udev/rules.d/80-net-setup-link.rules:5 Jan 23 15:01:30 debian10 systemd-udevd: ppp0: IMPORT builtin 'path_id' fails: No such file or directory Jan 23 15:01:30 debian10 systemd-udevd: Starting 'ifupdown-hotplug' Jan 23 15:01:30 debian10 systemd-udevd: Successfully forked off '(spawn)' as PID 1329. Jan 23 15:01:30 debian10 systemd-udevd: Process 'ifupdown-hotplug' succeeded. Jan 23 15:01:30 debian10 systemd-udevd: ppp0: Device (SEQNUM=1740, ACTION=remove) processed Jan 23 15:01:30 debian10 dccm: DEBUG: gudev_uevent_callback: received uevent remove for device /sys/devices/virtual/net/ppp0 Jan 23 15:01:30 debian10 systemd-udevd: ppp0: sd-device-monitor: Passed 298 byte to netlink monitor Jan 23 15:01:34 debian10 systemd-udevd: Cleanup idle workers Jan 23 15:01:34 debian10 systemd-udevd: Unload module index Jan 23 15:01:34 debian10 systemd-udevd: Unloaded link configuration context. Jan 23 15:01:34 debian10 systemd-udevd: Unload module index Jan 23 15:01:34 debian10 systemd-udevd: Unloaded link configuration context. Jan 23 15:01:34 debian10 systemd-udevd: Worker exited Jan 23 15:01:34 debian10 systemd-udevd: Worker exited Evident, SynCE use glib based gudev to monitor the udev events. Listen to the events "uevent" signal, to do that, attach a callback to this signal and wait for the notification. The USB device is not unplugged, no reason for signal "action remove". With Ubuntu 14.04 it works out of the box very well. Here comes my knowledge. I don't know how to get closer to the origin of the problem. I need to make the connection ppp0 /dev/ttyUSB0 stable. Any help or suggestion will be well received and greatly appreciated.