Photoshop: Problem Duplicating layer folders and pasting to new artboard

That one is annoying, but it's a different issue than what Ken and I are having.

(Though it does sound like João Dias also thought this was that problem)

I just noticed that if I use the mouse to drag the layer group in the canvas area into the art board area, the relative layout remains unaffected as one would expect.

The problem only happens for me when moving groups around in the layer panel, not in the canvas area.

Well, it's actually not anything with internal IDs that are attached to each layer. 
The recent bug was purely a problem caused by some cleanup we did in the 20.0 cycle to fix other issues reported by users over the past 3 years. Unfortunately, this got past us, but the duplication issue should be better in 20.0.1. Please try it out.

The recent issue was caused by a combination of auto-nesting and coordinate juggling. Using your example: When a group within a artboard B is duplicated, the XYWH of the group is supposed to be measured from the upper left of the containing artboard B. When the new group is created, it is positioned relative to a destination "container", either an artboard or the document canvas. (Digression 1: In artboard documents, the document canvas is hidden. It also changes size depending on document content. This allows you to spread artboards and content not in artboards all around as you do your designing.) 

The bug was that we picked the wrong destination container when duplicating within an Artboard B: we picked the document canvas, when we should have picked Artboard B. This caused the new group to be created with the XYWH relative to the canvas. Usually this will position the new group in the upper left of your workarea which just happens to be where Artboard A is located. (Digression 2: you can still see the bounds of the hidden canvas in the Navigator Panel if you are curious.) If you have just one artboard, the container offsets for the canvas and he source Artboard are the same which is why a portion of our basic testing did not show a problem. Anyway - At the conclusion of the new group creation, the auto-nesting code then fires: It first moves the group out of Artboard B because it is no longer visible within Artboard B, and then it autonests the group into Artboard A because with it's new coordinates it happens to overlap with Artboard A. And that's why you saw what you saw.

Cmd-J on a single layer bypassed this mechanism which is why that use case works even when working with multiple Artboards. Why there are two mechanisms for Cmd-J is an Official Mystery of Photoshop internals. There are also about 6 other ways to duplicate a Layer or Selection. Stuff like that happens when the code base is 28 years old. And yeah, we should find time to tidy that up.

Then cease releasing new Photoshops for next few years and rewrite original code finally, so you have clean start for new features which will be easier to fix if found buggy. Do not postpone it ! ;)