Good afternoon Jens (and Astrid) and welcome to the Events Calendar Support forum!
Thanks for reporting this. We are aware of these issues with the update to version 4.1 and we are really sorry for the hassle this might cause. We are actively working to solve these issues. I’ve linked this thread to the bug report in our backlog, so you’ll get notified here when we have some update or fix for this.
For now you can downgrade the plugins to version 4.0.7. You’ll find the past versions for our premium plugins in the download section of your account in this site (https://theeventscalendar.com/my-account/downloads/) and you’ll find the core plugin (The Events Calendar) past versions here:https://wordpress.org/plugins/the-events-calendar/developers/.
Thanks for the patience while we work on this.
Best,
Geoff B.