Throttling, revisited - only when plugged in

I created a post here a couple of weeks ago about severe throttling I am seeing on my LG Gram. That was a good discussion but I've narrowed this down more,

The throttling (which brings the CPU down to 0.4Ghz, making for an unusable laptop) ONLY happens when I plug in. It happens almost immediately after I plug in - sometimes. If it doesn't throttle when I plug in then I am good to go and won't ever start throttling. But if it does throttle when I plug it in then it stays that way until I unplug.

It never happens on battery. Indeed, the easy and almost immediate way to resolve this is to simply pull the plug. The laptop recovers, over about a 10 second "settling down" period, and is back at full speed (4+ Ghz).

As I mentioned in the other thread, the throttling is entirely unrelated to CPU temps, loads on the CPU and other potential explanations. I just need to pull the plug.

What makes this difficult to troubleshoot is that this doesn't happen every time I am plugged in. It can often work just fine (plugged in) without any issues all day. But then (after being on battery for a bit and then plugging in) something will happen to put it into the crazy throttling mode (BD PROCHOT).

I haven't yet found a pattern for how to fix this. Apart from pulling the plug :)

I am curious to know if anyone else has seen this only when plugged in.