Why is my pressure maxing out?

Three times in this graph my pressure rises to the maximum.
But they don't correspond with events or sustained leaks.

When and why does the machine decide to increase the pressure?

Pressure rises most strongly on snores and flow limitations and some breathing irregularities. If you enable the flow limitations graph, you might see a correlation with the pressure increases. You have the option to change what the maximum is. As long as you don't experience OA and excessive snores as a result of reducing the maximum pressure, you might consider doing that to prevent sleep disruption.

It increases because of warning signs that the airway is trying to collapse.....it's working at preventing the collapse and not necessarily fixing the collapse after it manifests itself in a flagged event.
When it is preventing we don't always see what it trying to prevent. Sometimes you can see it in the snores and flow limitation graphs (and sometimes you can't) but the machine is sensing a reduction in air flow for some reason and is trying to prevent further reduction. It's just doing its job and the fact you don't see much in terms of flagged events means it's doing a good job.