If it is an obvious bug, then it's likely other people would have noticed it as well. I've automated HPF without incident. Tried it again in case it was an X3e thing, but again, it worked. If this really had been a problem since X2, surely someone would have responded to your query whether anyone else had experienced this behavior.
If it's not an obvious bug, we would need more info. I'm not sure, for example, what this means: "The automation lane is clear, meaning there if wasn't one before for HPF control (cuz if there was an automation lane for HPF there's no change)
If it's pilot error, we would also need more info.