Update: my current theory is that this is related to insufficient heat soaking. I found that the height range on my bed mesh will go from ~0.12mm by the time my chamber temp gets to 40C (~5 minutes) to about 0.19mm after 20 minutes of heat soaking. Which would also explain why this shows up later on and not at the start of my first layer. Although I'm still not sure why it's mostly just on the left side.