When re-attaching all art/attachments to a new single bone, the order of attachments may change because the draw order is determined by the slot order in the hierarchy. To fix this, you can manually adjust the draw order in the Draw Order panel in Spine. This allows you to reorder the slots to achieve the desired visual stacking of attachments. Unfortunately, there isn't an automatic way to preserve the original order when re-parenting to a new bone, so manual adjustment is necessary.

I'm not sure if you're specifically talking about the draw order, or about attachments changing coordinates when you reparent them, or if something else is happening. Please also show us a gif or video of what you are doing. Also are you on the latest Spine version?

How are you performing this action? If I do the following, the order is respected:

1. Filter the tree on slots
2. Select all of the slots in the tree by selecting the first on top, then shift + click on the last oen to select every other slot
3. Save a selection of the slots with CTRL+1(CMD+1 on Mac)
4. Remove the filter on slots in the tree
5. Press 1 to recall the saved slots (Otherwise the bones are selected instead) (as an alternative also PagUp/Down works)
6. Move the slots in a new skeleton/under a new bone