Unable to Access SMB Share on NetBIOS Alias

So we have an ancient Win7 machine which has been used as a file server. This thing has come to the end of its life, and the 20-user limit is starting to hit us hard.

I have set up a FreeNAS server, and configured it with its own NetBIOS name, and added the old server's NetBIOS name as an alias. I see the alias on the network, but cannot access it and get System Error 53 (Network Path Not Found) when attempting to connect to the alias, but everything works fine when connecting to the defined NetBIOS name. What's going on?

EDIT:
Weird: even if I change the NetBIOS name in the FreeNAS web interface, I still can't access it from the new NetBIOS name, but if I change it back, everything works. smb4.conf attached (note it gets overwritten constantly by FreeNAS)

[global]
server min protocol = SMB2_02
server max protocol = SMB3
interfaces = 127.0.0.1 172.16.5.20
bind interfaces only = yes
encrypt passwords = yes
dns proxy = no
strict locking = no
oplocks = yes
deadtime = 15
max log size = 51200
max open files = 116768
logging = file
load printers = no
printing = bsd
printcap name = /dev/null
disable spoolss = yes
getwd cache = yes
guest account = nobody
map to guest = Bad User
obey pam restrictions = yes
ntlm auth = no
directory name cache size = 0
kernel change notify = no
panic action = /usr/local/libexec/samba/samba-backtrace
nsupdate command = /usr/local/bin/samba-nsupdate -g
server string = FreeNAS Server
ea support = yes
store dos attributes = yes
lm announce = yes
hostname lookups = yes
time server = yes
null passwords = yes
acl allow execute always = true
dos filemode = yes
multicast dns register = yes
domain logons = yes
local master = yes
idmap config *: backend = tdb
idmap config *: range = 90000001-100000000
server role = standalone
netbios name = FREENAS
workgroup = NEXT_ADVANCE
security = user
create mask = 0666
directory mask = 0777
client ntlmv2 auth = yes
dos charset = CP437
unix charset = UTF-8
log level = 1
wins server = 172.16.1.2


[shareddocs]
path = "/mnt/freenas01-troyvm-pool01.prod/shareddocs"
printable = no
veto files = /.snapshot/.windows/.mac/.zfs/
writeable = yes
browseable = yes
access based share enum = no
shadow:snapdir = .zfs/snapshot
shadow:sort = desc
shadow:localtime = yes
shadow:format = auto-%Y%m%d.%H%M-2w
shadow:snapdirseverywhere = yes
vfs objects = shadow_copy2 zfs_space zfsacl streams_xattr
hide dot files = yes
guest ok = yes
guest only = yes
 nfs4:mode = special
nfs4:acedup = merge
nfs4:chown = true
zfsacl:acesort = dontcare

EDIT 2:
Found out this is actually down to the old server name (T_REX) having a _, which is not an allowed character. Is there a way to allow unallowed characters in a share name?