TAdvWebBrowser - unsupported MIME type

I have an working implementation of the HERE Maps API for JavaScript which uses the TAdvWebBrowser on a Delphi form. I'm attempting to update this to use their latest rendering engine, but I'm encountering MIME errors like the below when the API attempts to retrieve vector tiles. This does not occur when running the same code in a standalone web browser.

Is there a restriction on the supported MIME types when running the embedded browser?

Error details from console:

BaseTileLoader: [H-74]: failed to load tile 81621711 InvalidArgumentError: ~Qf() (Argument #0 Mime type is not supported)
    at new C (mapsjs-core.js:39:376)
    at new Qf (mapsjs-core.js:130:473)
    at Co.o (eval at <anonymous> (mapsjs-core.js:89:72), <anonymous>:18:150)
    at ap.Pa (eval at <anonymous> (mapsjs-core.js:89:72), <anonymous>:47:49)
    at $o.o (eval at <anonymous> (mapsjs-core.js:89:72), <anonymous>:45:310)
    at q (mapsjs-core.js:313:405)
    at zk.get (mapsjs-core.js:315:495)
    at mapsjs-core.js:313:437
    at new Pd (mapsjs-core.js:79:955)
    at S.Ow (mapsjs-core.js:313:134)

Any reason for repeating all such development when there is already a solution we have fully developed in TMS FNC Maps:

Hi Bruno - the original development this is part of actually predates FNC Maps!