During testing, I just shorted the panel to load up the junction box. You get some interesting patterns that don’t show up under normal operation - apparently this is just “a thing panels do when shorted,” it highlights minor variances in the cells.
And the revised box, running cool. The “hot spot” to the right of the left main lead is a window to the back of the panel, so it’s seeing the back plastic - it’s not an issue in the box.
