It appears that null values are not handled well by scattergl. The data that is present is displayed as expected, for example 3 of 4 points are shown in the screenshot below. However mousing around the plot area throws a lot of errors from the hoverPoints function. For example, Uncaught TypeError: Cannot read property 't' of undefined.

Reproducible example:
https://jsfiddle.net/bhogan_mitre/u41pn9eo/
I believe this is the underlying function at fault: https://github.com/plotly/plotly.js/blob/master/src/traces/scattergl/hover.js#L15
Would it be appropriate to add some checks in that function on cd before trying to access cd[0]? I have also seen errors further down where it makes it past this line:
var stash = cd[0].t;
but fails here:
var x = stash.x;
I will note that this is only an issue with scattergl and not the normal SVG scatter.
Thanks very much for reporting!
Looks like this is regression from 1.45.0.
Things were working ok in 1.44.4: https://codepen.io/etpinard/pen/VwZgjom?editors=1010
It looks like it was working in 1.46.1: https://codepen.io/antoinerg/pen/mdbvrBx?editors=1010
and that the regression was introduced in 1.47.0: https://codepen.io/antoinerg/pen/BaBMLmq?editors=1010
Interesting. It's failing in 1.45.0 though: https://codepen.io/etpinard/pen/NWKoRMJ?editors=1010
Oh, I'm sorry, disregard https://github.com/plotly/plotly.js/issues/4212#issuecomment-534219458