It's not clear to me why management would become obsolete. Good management (the coordination of people, resources, and timelines) requires skill and is a science, and the efficiency we get from division of labour/specialization suggests workplaces would be better off if some workers specialized in management roles.
See, for example, Krupskaya:
We, Russians, have hitherto shown little sophistication in this science of management. However, without studying it, without learning to manage, we will not only not make it to communism, but not even to socialism.
Workflow optimization and employee morale will still be important under socialism.
Workflow optimization is just management of people/resources/timelines (and is present in non-repetitive jobs too): what processes aren't working well together, what were the root causes of issues we encountered, how do we fix these problems? This, too, gets better with experience and study and some workers should specialize in this sort of management.
Employee morale (and other aspects of emotional work) will also still be a relevant question under socialism: how do you balance a specific worker's development interests with the needs of the job, how do you manage interpersonal conflict, how do you build consensus for or mediate disagreement raising from decisions the group needs to make? Straight-up boring old motivation questions also do not disappear just because workers have a stake in the fruits of their labour.