HERE Maps Vector map in iFrame doesn't work - core.js issue

Question

I have an application created with FileMaker and implemented Here Maps as a routing feature. I'm able to show Here Maps in my FileMaker Pro 19 client, although when I want to show the same map on iOS (FileMaker Go 19) or on the web (FileMaker WebDirect) I get the /iframeheight.js resource not found issue: https://a.cl.ly/qGuR94no

I have to put the maps in the iframe to show it correctly. The interesting thing is that it does show correctly the Satellite view, Traffic conditions, Traffic incidents, but when I need to load Map View (default) the background is grey: https://a.cl.ly/o0u7rlyZ

Also the Raster map loads up correctly as well, but I can't make the default map view to load up. So looks like the issue comes up only for Vector map in iFrame.

I'd appreciate any ideas how it could be fixed. Thank you!