The <body> is generated 2 times (normally inside <li> tag of <head>) and makes render error.
The problem comes from New Relic.
- If the Episerver site is hosted in DXC, please request to install Azure Application Insight instead of New Relic.
- If the site is hosted in IIS like Everweb, please uninstall the New Relic and contact with New Relic support. There may be a released version that fixes the issue. You may consider to use another application to monitor the site or move your site to cloud environment (Azure, DXC...)