After upgrading to foreman version 3.8 we can no longer view configuration management reports in the web gui. The error from the logfile is in the attached logfile.

The "bug" has been introduced by the change https://projects.theforeman.org/issues/36219

I was able to fix it temporarily by adding Symbol to the permitted_classes in the file /usr/share/foreman/app/models/report.rb:

    YAML.safe_load(read_metrics, permitted_classes: [Symbol, ActiveSupport::HashWithIndifferentAccess]).with_indifferent_access