Why does low-speed preignition occur at low rpms and high load a.k.a engine lugging?
At low RPM with an open throttle ( lugging) , there is nearly atmospheric pressure in the manifold . Then you get maximum compression in the cylinders so if the fuel octane is not high enough for that compression , you get preignition. Of course if the timing is too advanced you can also get preignition even with good octane.
LSPI is occurring on many late model direct injection w/turbo cars. It's pretty serious and the car companies and oil companies are working on a solution for the problem. The current theory is that the high pressure squeezes oil droplets out from the ring lands and causes them to ignite and cause detonation. See this post on LSPI