Benoît Brayer added the comment:
Please find what Django's devs have done to parse cookies:
https://github.com/django/django/commit/93a135d111c2569d88d65a3f4ad9e6d9ad291452
I hope this might help to find a solution.
--
nosy: +brayer.b
New submission from Benoît Brayer :
Using python3.8.5, SimpleCookie parser seems to be unable to load the cookie
string when a json string is used inside one of the cookie values.
I did not try to replay using other python3 versions yet.
Please use the following code to replay the bug