Sort of, this was a weird case.
We discovered that distribution lists were not flowing at a site due to email server security setup.
There was a 3rd party Exchange admin. who only managed to allow individual email addresses to flow from Vantage. (addresses for the internal domain only and distro lists would still fail).
Temp workaround was to use the individual addresses.
And that is when I discovered there issues if too many addresses were used.