Starting in versions 1.625.3 and 1.641, Jenkins restricted what kind of content could be displayed when serving static files. This can impact how HTML files archived using this plugin are displayed. See Configuring Content Security Policy for more information.
As a workaround you can relax default CSP rules in Jenkins configuration.
More details about CSP in Jenkins you can find in documentation.
If you're using HTML Publisher plugin and HTML report looks ugly then you should manually relax default Content Security Policy rules.
From HTML Publisher plugin wiki:
As a workaround you can relax default CSP rules in Jenkins configuration.
More details about CSP in Jenkins you can find in documentation.