tohsakarat if there was an error, it should be logged automatically to <flarum>/storage/logs folder.
Or maybe there's a PHP warning/error (not exception) outputted when the queue worker processes the job. In that case it might be logged in the output file of the daemon or CRON job it runs with, or in the system PHP log file.
I'm not sure where/how redis stores the queued jobs, but if you see the job disappearing from the queue, it must mean it was processed.
One last option is that perhaps everything runs without any error, but the server that processes the redis jobs cannot send emails to the internet and fails silently because of a firewall rule or internal email relay. If the jobs run on the same server as the forum, this should never be an issue unless the process runs inside a "jailed" environment.
