[Fixed]-Save/Restore GroupResult with Celery in Django: None returned

You should save() GroupResult if you have plan to use it later.
Then you can restore it by providing GroupResult.id to restore() method:

from celery import group, result
from app.tasks import foo, bar

group_result = group([foo.s(), bar.s()])()
group_result.save()

restored_group_result = result.GroupResult.restore(group_result.id)
print(restored_group_result)