When I was trying to migrate my site and export the database I realised that the cache_form field is enormous. According to suggestions I have found online the proper way to solve this is to run cron. So I try to run cron by going to the admin/config/system/cron page, and in there it said that cron was last run 3 weeks ago.
When I press run cron or when I visit the link with the cron key provided in that admin/config/system/cron page, they have both led me to user/0/edit instead of running cron. I did a quick search among the files I have made changes to in the site directory in these three weeks and none of them are leading to user/uid/edit. I wonder what else can I do to solve this properly?