Thanks for the report!

As well as { autorange:'reversed' }, I observed that the issue also exists using
{ ranges:[a, b] } when a > b.

The bug is actually related to the modification of scale parameter within the vertex-shader of regl-line2d library: node_modules/regl-line2d/miter-vert.glsl
For any reversed axis the scale value was replaced by positive epsilon: 1e-6 by the max function. This resulted in display of an almost horizontal/vertical line (depending on which axis was reversed).

The users may also wait for additional tests to be completed and possibly a new release of the mentioned library.

In the meantime using the following function inside the vertex-shader file could help fix the issues e.g. reversed bounds in 2D space.

float repaireScale( float a ) {
	float b = a;
	if (abs(b) < MIN_DIFF) {
		if (b < 0.0) b = -MIN_DIFF;
		else b = MIN_DIFF;
	}
	return b;
}

void main() {
	vec2 aCoord = aCoord, bCoord = bCoord, prevCoord = prevCoord, nextCoord = nextCoord;

	vec2 newScale = scale; 
	newScale.x = repaireScale(newScale.x);
	newScale.y = repaireScale(newScale.y);
  
	vec2 scaleRatio = newScale * viewport.zw;
  
  ...

}