- Plesk Onyx for Linux
- Website preview is unable to load some CSS files.
- There are warnings regarding mixed content in Browser Console.
- Preview link is opened via HTTPS.
- There is a default site for the corresponding IP address set in Tools & Settings > IP Addresses > 203.0.113.2.
- Default site has enabled a redirection from HTTP to HTTPS.
Plesk bug #PPPM-8687 which is planned to be fixed in upcoming Plesk updates.
As a workaround:
- Log in to Plesk GUI
- Go to Tools & Settings > Website Preview and select another Website Preview option or disable HTTP to HTTPS redirection in the default site assigned to the IP address.