I've had an ongoing issue with my web application in mobile Safari in all versions of the JavaScript API from at least 4.13-4.23. Occasionally, I receive the JavaScript error "Cant find variable: require", followed by "null is not an object (evaluating 'Z.parentNode.insertBefore')". These errors are thrown in the ESRI libraries.
After this error, the map fails to load. This doesn't occur all the time and I can get the map to load if I refresh the page several times. It only occurs in mobile Safari from what I can see. I assume that something with Node is not loading when I try to load the ESRI library but I don't know how to get around this.
I am loading the ArcGIS libraries from https://js.arcgis.com/4.23/.
@MikeVare you able to reproduce the issue with this codepen: https://codepen.io/andygup/pen/LYdYybe?