mglae I'm confused now. On my RPi3B+ the lsusb with no attached USB devices is:
QuoteBus 001 Device 004: ID 0424:7800 Microchip Technology, Inc. (formerly SMSC)
Bus 001 Device 003: ID 0424:2514 Microchip Technology, Inc. (formerly SMSC) USB 2.0 Hub
Bus 001 Device 002: ID 0424:2514 Microchip Technology, Inc. (formerly SMSC) USB 2.0 Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
No Ethernet device on the list. Are you saying RPi3B and RPi3B+ handle internal sub-devices differently?