Sim loading sometimes sticks in `Sim State: Lobby` with no Select Role screen

[connorjak]

Describe the bug
A Python System is being waited upon by the main Compute_Server process to finish its Load phase, but it actually is already loaded so some other bug is happening. The Unreal client shows the sim as being in Sim State: Lobby, and relays the message from the Compute_Server main process that it hasn't heard one or more Python Systems have finished Load yet. After 60 seconds, the sim times-out and crashes.

To Reproduce
Steps to reproduce the behavior:

1. Start any sim with a Python System
2. ~5-15% chance of this bug happening

Expected behavior
Reliable startup sequence, or reliable handling of errors that cause the sim to crash instead of timing-out.

Desktop (please complete the following information):

• OS: Windows 11
• Platform Version 0.52.2, but this has been happening since at least as far back as 0.40