More accurately, there's no one person that is both held responsible and empowered to make sure that part of the process works.
By analogy to "power vacuum", it's tempting to call this pattern an "ownership vacuum".
Is there a more common term?
There was an important job to be done and Everybody was asked to do it. Everybody was sure Somebody would do it. Anybody could have done it, but Nobody did it. Somebody got angry about that, because it was Everybody's job. Everybody thought Anybody could do it but Nobody realized that Everybody wouldn't do it.
It ended up that Everybody blamed Somebody when Nobody did what Anybody could have done.
It doesn't work that well. Power vacuum is called that way because there's a tendency for the vacuum to be filled by anyone as soon as possible. On the other hand, lack of ownership in a company can persist for much longer if left alone.
But there's a different tendency that is also similar to various physical processes.
Imagine water flowing out of a bottle. It gulps down in parts instead of flowing steadily because of the decreasing air pressure inside the bottle.
A similar thing happens with these ownership gaps. Problems pile up until the person least capable of tolerating the stress decides that enough is enough. That person will temporarily take the responsibility upon themselves and clean up the mess, and so the process will start over.
The area isn't seen as valuable, so no one wants to wind up stuck there. Really, it's a leadership problem, because by adding in some compensation or praise or prestige, managers can create arable land.
Seek responsibility, not power.
After a contractor failed to complete a program to update and combine numerous IT resources for numerous departments the state of Minnesota brought a program called MNLARS in house.
Among the failures that ended up being super costly, there was nobody really in charge of the whole program, and many people who were decision makers didn't even know work was waiting on them making decisions / they didn't even know they had the power to make those decisions. In short nobody was at the wheel...
I don't know if there is a very clear term for that, but I really like your "ownership vacuum".
This is almost always a result of an institution failing to reward folks for doing routine maintenance tasks and only providing incentives for new stuff.
Seriously, somebody must be over that process, even the CEO if nobody else will claim it. They either need to handle it, or delegate it to someone to handle. If there is a vacuum, accountability rolls up to the leader.
I agree that there's always someone responsible for this, even if it's the CEO who fails to empower subordinates to do this at their level.
It could be that many other problems boil down to parts of process not being owned by anyone. That is, that all management problems are ownership gaps in disguise. I'm not sure.
With only rare exceptions, it was nobody's job to answer the phone. During busy periods, it would ring and ring and ring.
I think it does come down to communication and management.