It is unlikely the changes in HTTPS functionality depend on a switch to new CSS cascading engine.

In order to find the issue reason I would recommend to do the following:

PD4ML supports so-called custom resource loaders.

Try to implement a debug version of HTTPS loader. I’ve attached our standard SSL loader implementation, which could give you some implementation ideas.

Please take into account: WebSphere and Weblogic implement their own versions of HTTPS protocol, and the implementations are not derived from the standard API.