I think we're having an issue with precision for a visual variable on iOS.
If you access the fiddle at https://jsfiddle.net/tograh/um6rjL4k/, you can click on "animate" to see a simple blue marker pass across map.
There's an opacity visual variable on the field "year". That field is a moment (i.e., momentjs) value representing epoch milliseconds for the years 2000-2009.
If I set the values of the opacity visual variables to match those epoch milliseconds, then the animation plays fine in my desktop's browsers, but it does not display on my iPad (iOS 12.1.1) in Chrome or Safari.
However, if you alter line 45 to use the field "yearSmall" instead of "year", it will divide "year" by one-hundred million, and that'll animate fine.
I'm trying to understand how I have transgressed. I think the values themselves are accurate. (They're being dumped in a console.debug().) Would anyone have any pointers?