>Summary :
The bug is exist long time since 1.14 official version. I've never seen its going to be fixed, so i create a new ticket in order there's no one who reported it. When i made skinpack via texture pack using render_controller, i cant merge 2 geometries into 1. In 1.14 beta and earlier than that, you can merge 2 Geometries by adding ":" symbol.

>Step To Reproduce
1. Make merged geometry with ":" to merge.
2. Define the geometry throug entity.json
3. Define it using render_controller
4. Apply the Resource_pack.

>Expected Result :
1. The skin appear
2. The Geometry Loaded

>Observed Result :
The first thing i do is to make 2 Geometry codes and then at the one of them, im adding the ":" symbol. So the identifier name will be like this :

*  "geometry.male2:geometry.male1": {*

And then visualizing it via entity.json :

    {
      "geometry": {
        "default": "geometry.male1",
        "cape": "geometry.cape"
      }

Its turn out that the Geometry doesnt loaded and make the skin Invisible. At first i think there's some changes inside the Minecraft environment, so i decide to define it once again at the entity.json like this :

    {
      "geometry": {
        "default": "geometry.male1:geometry.male2",
        "cape": "geometry.cape"
      }

The result was still the same as before. The skins turns out blank and invisible. Already tested when using Custom Entities, the Geometry of defined entity doesnt load up and make the Entity was also invisible. Hope this one gets fixed because its really helpfull when making base geometry and adding Mobs variant geometry inside of it with just merging 2 geometries.

At the end, i need to separate the geometry and made the geometry independent to make it work. As you can see at the Attachment there's some skin that visualize and not Invisible (Because the Geometry already separated and Independent) while the Invisible one exist because as i tell earlier that the Geometry was merged with another.

>Reality Result :
1. The skin become Invisible
2. The Geometry doesnt loaded

>Issue Update :
On the latest version, the merged geometry skin will only can be seen by the owner and others cant see that. Here's the taken example from each perspective

• Owner Perspective (Device 1)
  The merged geometry Resource Pack seems fine and its appear perfectly

Yet, while on the Persona Editor.. The Player Render Controller doesnt work and make the Persona showing the Loading button.

• Other Player Perspective (Device 2)
  The Merged Custom Geometry Reource-Pack doesnt load up even though its sharing and using the same Resource-Packs.

The pack that used on the testing is : MCWig - Anime (With some edits)
Tested using Minecraft version : 1.16.20 Official & 1.16 Beta