CPU count and slow Windows VM

I'm helping someone trouble-shoot a sluggish Windows 11 VM running under bhyve (FreeBSD 14.1) related to the number of vCPUs. With 1-2 vCPUs, the VM's performance is reasonable, but adding 8 or more vCPUs makes the VM nearly unusable because even moving the mouse takes minutes.

Before I dig into this, do these symptoms sound familiar? I did find a mention on the wiki (1):

    Only one or two VCPUs should be used during installation but this number
    can be increased once Windows is installed

Is there something missing from bhyve's emulation that causes this?
TIA

--chuck

(1) https://wiki.freebsd.org/bhyve/Windows