Nonstop errors on breakpoint: getornull: Condition "!id_map.has(p_rid.get_data())" is true. Returned: __null

[Error7Studios]

Godot version:
3.2.4 RC 2 and 3.2.4 RC 3

OS/device including version:
Windows 10, GLES3, GeForce GTX 1050 Ti/PCIe/SSE2

Issue description:
Under certain conditions, (not sure exactly which), I get spammed with this error:

E 0:00:12.010   getornull: Condition "!id_map.has(p_rid.get_data())" is true. Returned: __null
  <C++ Source>  ./core/rid.h:160 @ getornull()

Steps to reproduce:
Do as shown in this example video.

1. Run game.
2. Select Move
3. Move next to demon.
4. Select Attack
5. Watch errors pile up when the code hits a breakpoint

Controls:
- Arrow keys: Move cursor
- Enter: Select menu option / Select cell to move character to
- Escape: Quit

Minimal reproduction project:
getornull error.zip

[Calinou]

Duplicate of #38229.