Chart default is required podAntiAffinity on hostname plus RollingUpdate 25%/25%, which is maxUnavailable=0 at replicas=1: the new pod stays Unschedulable while the old one lives, and the old one never leaves while the new one is not Ready. Null the affinity (an empty map deep-merges with the default and keeps the rule) and set maxSurge/maxUnavailable to 1.