Looking at the details you provided, it’s not clear to me where in the Discourse code the error is being triggered. Are there any details in the “info” or “env” tabs on the error page? There’s also a “share” button on the bottom right of the page that will display all error details.
I’m not certain the error is related to the issue, but it seems that something’s going wrong with background jobs (sidekiq) on your site.
There might also be useful information on your site’s /sidekiq page. As an admin user, you can view it at https://community.lezismore.org/sidekiq