(Henry Spencer) writes:

[...]

Correct. As the value of the eccentricity wanders around randomly, the
orbit gets less or more elliptical. If it ever gets elliptical enough
that its lowest point is at or below the surface, it's game over. For a
low lunar orbit, mascon effects are strong enough that this tends to
happen fairly quickly.

(It is possible that there are stable low orbits around the Moon, where
the mascon effects cancel out, at least for a while. We don't know enough
to predict where they might be, because we don't have good gravity maps of
the lunar farside. All gravity mapping to date has been based on tracking
from Earth, which is impossible over most of the farside. You can get a
little bit of information by looking at how the orbit has changed when the
spacecraft comes back into view, but not very much. There have been many
proposals to do farside gravity mapping, using a pair of satellites and an
intersatellite radio-tracking link, but so far it hasn't been done.)

What this means is that the orbital environment around the moon is chock
full of opportunities and hazards for spacecraft spending a bit of time
there, and that accurate charts of its gravitation field will be a
precious thing for navigators to have. So the low grade rumble you're
hearing throughout this discussion is a wish for some attention to be
paid to acquiring this information.