I’ve found the issue and the resolution:
support for TCP wrappers isn’t compiled in vsftp binaries found in SLES and Redhat.
The installer must be modified to not output tcp_wrappers into the vsftpd.conf
This has resolved this issue in SLES.
I’m guessing ntcp_wrappers=$tcpwrappers\n$seccompsand is configured to output disabled if certain versions redhat? but that didn’t trigger for SLES
Thanks very much for your help @Sebastian-Roth