This post seems similar to your situation. I recently encountered a problem upgrading to Ubuntu 20.04 and it was the captcha even though it was previously installed and running fine.
sudo apt -y install python3 python3-pip python3-pil python3-ldap python3-urllib3 libpython3.8 python3-setuptools python3-mysqldb python3-memcache python3-requests ffmpeg
sudo apt install python3-django-captcha