Samba Audit no filename appear

Question

I'm using samba to provide shares to users. The sometimes claim their files have mysteriously disappeared so I am keen to track deletions.

Thus I set up full audit. Everything works, except the audit log is often missing the file name or has some sort of mystery code. For example;

Dec 12 17:46:04 server1 smbd_audit:
shared|shared|192.168.x.x|matt1|shared|2016/12/12
17:46:04|server1|file_id_create|ok|802:28200da:0

The last item should presumably be a file name. Why is there a number instead? The relevant parts of smb.conf follows

[homes]
   comment = Home Directories   directory mask = 0775
   browseable = yes
   read only = no
   create mask = 0775
   directory mask = 0775
   valid users = %S
   writable = yes
   vfs objects = recycle
   recycle:repository = .RecycleBin
   recycle:keeptree = yes
   recycle:exclude = *.tmp, *.bak

   vfs objects = full_audit
   full_audit:prefix = %u|%U|%I|%m|%S|%T|%D
   full_audit:success = mkdir rename unlink rmdir open
   full_audit:failure = none
   full_audit:facility = LOCAL5
   full_audit:priority = NOTICE