Dynamic variable resolution in array parameter

SUMMARY

I have an action workflow which at some point installs a pack:

 - name: "echo_var"
    ref: "core.local"
    parameters:
      cmd: "echo {{ work_dir }}/{{ extract_project_name.result[\"project_name\"] }}"
    on-success: "install_pack"
    on-failure: "remove_folder"
 - name: "install_pack"
    ref: "packs.install"
    parameters:
      packs:
        - "file:/{{ work_dir }}/{{ extract_project_name.result[\"project_name\"] }}/{{ pack_location_relative_path }}"
    on-failure: "clean_up"

I recon within the array-string the extract_project_name.result[\"project_name\"] is not resolved, leading to an erroneous input for the install_pack step.
As a result the step is not executed at all, I don't even see traces of invocation. The previous action (echo_var) works just fine, and resolves the variable perfectly.
After this the execution continues with the remove_folder step (as pointed to by the echo_var step.

Note that this

STACKSTORM VERSION

st2 3.1.0, on Python 3.6.9:

OS, environment, install method

• Ubuntu 18.04.4 LTS
• one-line install (curl -sSL https://stackstorm.com/packages/install.sh | bash -s -- --user=st2admin --password='Ch@ngeMe')

Steps to reproduce the problem

• Create a basic python action, which returns an object (such as {"message": "somemessage}) and then try to use its result in the action chain as described above.

Reproduce the action-chain workflow with a basic Python action returning an object, then trace dynamic variable resolution for the array-valued packs parameter. Compare it with the working scalar cmd parameter and verify that the resolved pack path reaches the install_pack step without triggering on-failure.