Help understanding "propagating changes to other nodes"

Hello all,

Im currently working on building UI for a preset / cue system for touch and have run into a problem which I am trying to understand more thoroughly.
I will post a re-creatable scenario once I have found one but basically I am running into a problem that when I select a item from a list Comp, and subsequently trigger various other stuff in the project to actually trigger the cue, I am getting a massive CPU spike 40ish ms which is reported in the performance monitor as “propagating changes to other nodes”.

FYI I get this even if I remove the reference to it further up the container chain so its not actually triggering much.

I would love to understand what that actually means as I have tested every step in the chain and nothing I can see warrants that spike.

In short what does “propagating changes to other nodes” actually mean and why might it take sooooo much cpu time.

Sorry if this is general but I at the stage of confusion, even to build a re-creatable file to share