The LED BF2 lights (continuously) not only in the case of an obvious bus fault (no physical connection to a subnetwork/switch), but also if IO or CBA network nodes are connected with the configured and networked PROFINET IO system ("Rail" visible in HW Config), which do not support 100Mbit/s full-duplex mode or if no PROFINET IO nodes are configured.
In many cases the PROFINET connection is used exclusively as CBA interface (e.g. communication to HMI or host system) or as programming interface. If this is the case, then an existing PROFINET IO system should be deleted in the HW Config (Fig. 1) or at least disconnected (Fig. 2). In this way you avoid the BF2 LED display.
When making the change described above, make sure that the interface remains in the "Networked: yes" state (Fig. 3).