If you set a nonexistant address for interfaces in smb.conf nmb will silently die, causing netbios lookups (and possibly other functions) to fail. However smbd continues to run, providing some aspects of samba file sharing.
# Configure Samba to use multiple interfaces
# If you have multiple network interfaces then you must list them
# here. See the man page for details.
interfaces = 192.168.1.10/24 192.168.2.10/24
## 192.168.2.10 doesn't exist (it was infact an old interface I'd previously removed).
Samba should run normally, and ignore the non-existant interface (possibly warning about it).
nmbd silently dies, smbd spawns two instances (one for each IP).
This is a known issue, yet I don't know what upstream has to say about this.
Please increase your parameter "log level" and attach your /var/log/samba/log.nmbd
I think this behaviour is more a "feature" than a bug, however I suggest you to open a bug in samba bugzilla 
Please reopen if this still affects samba-4