The only system files used by Netdrive and the Samba plugin are ndpsmb.dll and smbcln49.dll (and things like libc, et al).
Thanks Paul, I went looking in the NDFS directory and found NDCTL.LOG which gave:
NetDrive for OS/2(R) Control Program version 3.1.5.865 Apr 06 2017
NDFSDIR environment variable found: E:\Programs\NDFS
NetDrive working directory is E:\Programs\NDFS
File system driver name is NDFS32.
NetDrive configuration file 'E:\Programs\NDFS\ndctl.cfg' has been processed.
Exclusive Samba Use
[ local] internal plugin has been initialized.
NDF0033: The system can't load the module: SMBCLN49
NDF0029: [ ndpsmb] plugin has not been loaded.
NDF0007: The system error is SYS0002
Initialization completed. The control program is running.
So it appears that SMBCLN49.DLL is missing. Searching for it brings up a blank, I can only assume that the ArcaOS 5.0.4 didn't install it when it updated the ndplugs directory unless it is supposed to be somewhere else.