Orbiting and landing on non-sperical objects
For bodies small enough to be non-spherical, the mass is relatively low (as an example, Rosetta's bounces took a long time - it touched the surface at 15:34, 17:25 and 17:32 GMT comet time) but the centre of mass is still the point the lander will orbit.

So a chaotic orbit is not a problem here

What will be problems are:


trying to arrange for the lander's velocity to match that of the landing site. For example if the body is spinning rapidly and an outcrop spins round into the path of the lander that could end badly
staying on the surface - Rosetta tried to use harpoons. Another proposed solution was a low powered rocket pointing upwards
while small bodies won't have an atmosphere as such, outgassing and dust can cause problems


I'm assuming 1 is the one you are most interested in here. The solution Rosetta favoured was to pick a site that was on one of the outer surfaces, rather than on the 'neck' of the comet, as this offered the cleanest route to landing. A landing on the neck would have necessitated flying into a channel on a spinning body, and that would make the calculations much harder.