Code 500 when upgrading self hosted server from 3.12.2-ee to 14.6.5-ee.0

I’m running a self-hosted GitLab server and I’m trying to migrate from version 13.12.2-ee to the latest version 14.6.5-ee.0.
Following the upgrade path shown on this page, I went first to 14.0.0-ee but something went wrong and the initialization keeps running indefinitely and the interface is showing a 500 error code
I just ran the commands

gitlab-ctl tail
gitlab-rake gitlab:check --trace
gitlab-rake db:migrate:status --trace

and I was wondering if somebody could take a look and perhaps give me a clue on how to proceed.
Thanks in advance.