I can no longer replicate the ignoring of manual migration request, as it clearly states conflict with strict negative affinity — as you detailed. Maybe it was fixed with an update to PVE or propagation to the browser UI.
I think it could be...
HA node affinity offers the strict option to specify whether a resource requires the condition, or (not strict) prefers it. The new HA resource affinities, especially negative, should offer it as well.
With an example load of 3 VMs running the...