[Bug] render on SubprocEnv results in uninformative error

[jelledouwe]

🐛 Bug

When running ik_box.py example from eagerx_interbotix with n_procs > 1, calling .render() results in errors.

To Reproduce

In ik_box.py in eagerx_interbotix set n_procs to 2 (or more).

Then call train_env.render("human").

Expected behavior

A clear and concise description of what you expected to happen.

Expected behavior: either render or meaningful error.

System Info

Describe the characteristic of your environment:

• Describe how the library was installed (pip, docker, source, ...): pip
• Versions of all EAGERx packages installed: eagerx == 0.1.32, eagerx_interbotix == 0.1.8
• Python version: 3.8
• Gym version: 0.21.0
• Versions of all relevant libraries

Additional context

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Checklist

• I have checked that there is no similar issue in the repo (required)
• I have read the documentation (required)
• I have provided a minimal working example to reproduce the bug (required)