I tried that too, but it still complains about an unsupported CPU in the new cluster. Even if I leave the cluster level at 4.2, if I update the host to 4.3 it can't activate under a 4.2 cluster.
Makes me think something changed in how it verifies the CPU support and for some reason it is not liking my EPYC systems.

On Sat, Feb 9, 2019 at 10:18 AM Juhani Rautiainen <juhani.rautiainen@gmail.com> wrote:
On Sat, Feb 9, 2019 at 7:43 PM Ryan Bullock <rrb3942@gmail.com> wrote:
>
> So I tried making a new cluster with a 4.2 compatibility level and moving one of my EPYC hosts into it. I then updated the host to 4.3 and switched the cluster version 4.3 + set cluster cpu to the new AMD EPYC IBPD SSBD (also tried plain AMD EPYC). It still fails to make the host operational complaining that 'CPU type is not supported in this cluster compatibility version or is not supported at all'.
>
When I did this with Epyc I made new cluster wth 4.3 level and Epyc
CPU. And then moved the nodes to it. Maybe try that? I also had to
move couple of VM's to new cluster because old cluster couldn't
upgrade with those. When nodes and couple problem VM's were in new
cluster I could upgrade old cluster to new level.

-Juhani