Good afternoon Jonathan and welcome to the Events Calendar Support forum!
Thank you for reaching out to us.
We are sorry to hear about the 404 error message impacting the link to see all of your recurring events. I would love to help you with this topic.
We apologize for the inconvenience caused by this glitch and we are actively working on a fix for this.
Unfortunately, I cannot commit to a release date for a fix at this point.
But you will be contacted as soon as there is one.
Thank you for your patience as we see this through.
In the meantime, there is a workaround to get your site working again.
Using Poedit, you can remove the translation for the “all” string (alle).
This will work, as you can see here http://www.coffee.de/schulung/solidworks-fuer-3d-umsteiger-schulung-3-tage/all
Best regards,
Geoff B.