Hi @Thorbenl, I had a similar problem, but it turned out the virtualenv stored in my cache wasn’t compatible with the new images. All you should need to do here is change your cache key. (One good practice is to have a version number in the key so it’s easy to change.)
Here’s an example from a project I maintain: Upgrade to new CircleCI convenience image by Mr0grog · Pull Request #763 · edgi-govdata-archiving/web-monitoring-processing · GitHub