When using the plotly-cartesian in place of the plotly distribution in the latest version (1.51.3, also reproducible in 1.51.1), for some inputs the histogram bars are incoherently laid out on the horizontal axis.
Some other inputs do not seem cause that issue.
The problem does not appear when substituting https://cdn.plot.ly/plotly-1.51.3.js.
Minimal reproduction of the issue
https://jsfiddle.net/c8gfb6rp/2/
var x1 = [1,3];
var x2 = [1,20];
var trace1 = {
x: x1,
type: "histogram",
};
var trace2 = {
x: x2,
type: "histogram",
};
var data = [trace1, trace2];
var layout = {barmode: "stack", height: 200, width: 400, margin: {t:30, b:30}};
Plotly.plot("plot", data, layout);
Screenshots
Here is what it looks like in the jsfiddle above.
Using plotly-cartesian (bug):

Using plotly (expected behavior):
