Cannot inherit from UnityEngine.XR.WSA.SpatialMappingCollider anymore

Hello all,

admittedly I have not tried this piece of a code for a few releases (possibly over a year)... so apologies if the problem was introduced BEFORE 2018.3b already.

I was inheriting from UnityEngine.XR.WSA.SpatialMappingCollider to override
OnSurfaceDataReady to define my own CustomSpatialMappingCollider
which I could do just fine before and seemed to be a great approach for what I wanted to do.

Now trying to do that, I receive the error:
"
'CustomSpatialMappingCollider' is missing the class attribute 'ExtensionOfNativeClass'!
"
trying to add the attribute does not seem to work as said attribute is inaccessible (internal sealed class).

Please advise - why don't you let me derive from SpatialMappingCollider anymore?
When was that change introduced? Was that change documented anywhere?

Any suggestions how to fix the issue?

Kind regards,