Debugger show large variable as [null] when getting Image from Viewport texture (the reference still works)

[bitsycore]

Godot version:
Issue in 3.2 and and 3.2.rc1
No issue in 3.1.2

OS/device including version:
Tested on Windows on two computer but the bug doesn't appear in 3.1.2 so I didn't tried in another OS because I assumed it's not a OS related issue

Issue description:
When I get the image from the texture of an instanced Viewport the resulting image (duplicate() or not) appear [null] in the debugger but print() actually print it's ID and the use of this var work.

Even other var appeared to be [null] in the debugger but the only problem I isolated was the viewport one. (I'll link a project with the viewport bug)

Steps to reproduce:
get_texture().get_data() from a Viewport inside your scene and assign it in a var

Minimal reproduction project:
Isolated Viewport
Bug-null-ref-debugger.zip

Another little project with this issue but when I was writing that issue and changing project multiple time with the minimal it work now (but the minimal still bug)

https://github.com/Coldragon/godot-voronoi-shader-generator

The bug is inconsistent for me now exept for the minimal project, it's really weird

edit : you can see the conversation I got with another user from the Discord
https://discordapp.com/channels/212250894228652034/477544613511692358/684839269033967639

[baptr]

I updated the original MRP to work at HEAD and confirm this matches #74148:

Fresh MRP: 36801.zip

With:

@onready var viewport = $SubViewport

func _ready():
	var tex = viewport.get_texture()
	print(tex)
	var img = tex.get_image()
	print(img)
	var dims = img.get_size()
	print(dims)
	var size = img.get_data().size()
	print(size)
	pass # break here

Locally I get:

Output:

<ViewportTexture#-9223372010313219669>
<Image#-9223372010229333471>
(1024, 1024)
3145728

Debugger errors:

W 0:00:00:0738   Node2D.gd:14 @ _ready(): Variable img too large to serialize for debugger: 3145964 > 1048576
  <C++ Source>   core/debugger/debugger_marshalls.cpp:83 @ serialize()
  <Stack Trace>  Node2D.gd:14 @ _ready()

[Calinou]

Closing in favor of #39465, as this is due to the same cause.