Found this post from 2017 listing the (then) icons:
Not sure what the icon set was in 2017, but it appears to be an issue with plotly.js. You can create a js plot with the following and get a warning from mapbox.
<head>
<script src="https://cdn.plot.ly/plotly-2.29.1.min.js" charset="utf-8"></script>
</head>
<body>
<div id="myDiv">
</div>
<script type="text/javascript">
var config = {mapboxAccessToken:"Your Token"}
var data = [{
type:'scattermapbox',
lat:['45.5017'],
lon:['-73.5673'],
mode:'markers',
marker: {
size:14,symbol:'cross'
},
text:['Montreal']
}]
var layout = {
autosize: true,
hovermode:'closest',
mapbox: {
style:'outdoors',
center: {
lat:45,
lon:-73
},
pitch:0,
zoom:5
},
}
Plotly.newPlot('myDiv', data, layout, config)</script>
</body>
Iβll see if I can come up with a reason.