interesting note, that this seems to not happen if it's a whole thousands number
ie: 3300 does it, but 3000 or 4000 does not (they display a non-segmented bar)

(I don't know anything about C++ so I don't know why I'm here — for fun, I guess)

This must be here:

		// If the flagship has a large amount of fuel, display a solid bar.
		// Otherwise, display a segment for every 100 units of fuel.
		if(fuelCap <= MAX_FUEL_DISPLAY)
			info.SetBar("fuel", flagship->Fuel(), fuelCap * .01);
		else
			info.SetBar("fuel", flagship->Fuel());

If it's showing * .01 of a bar for each unit, that would cause this, right?

It might make more sense for this to be size related to your cap instead of per 100 units. 3300 * 0.01 is 100 units, 33 times.

But const double MAX_FUEL_DISPLAY = 5000.; 🤔

(I don't know anything about C++ so I don't know why I'm here — for fun, I guess)

This must be here:

endless-sky/source/Engine.cpp

Line 741 in f3430b6

info.SetBar("fuel", flagship->Fuel(), fuelCap * .01);

		// If the flagship has a large amount of fuel, display a solid bar.
		// Otherwise, display a segment for every 100 units of fuel.
		if(fuelCap <= MAX_FUEL_DISPLAY)
			info.SetBar("fuel", flagship->Fuel(), fuelCap * .01);
		else
			info.SetBar("fuel", flagship->Fuel());

If it's showing * .01 of a bar for each unit, that would cause this, right?

It might make more sense for this to be size related to your cap instead of per 100 units. 3300 * 0.01 is 100 units, 33 times.

But const double MAX_FUEL_DISPLAY = 5000.; 🤔

The MAX_FUEL_DISPLAY value determines how high the fuel capacity can be before the fuel bar will be displayed as a single solid line instead of a segmented line.

The fuelCap * .01 calculation is determining how many segments there should be in the bar. One segment for every hundred units of fuel. It doesn't affect how much of the bar is drawn.
You can find the definition of SetBar in Information.cpp.
Look in Interface.cpp at the method Interface::BarElement::Draw to see what is done with those values, and the LineShader class for how the bar is actually drawn.