I have a fresh Portal 10.5.1 installation on Linux CentOS 7.3. Calling the portal on http://machine.domain:7080/arcgis/home the page appears but immediately switches to https://machine.domain:7443/arcgis/home/createadmin.html and the page shows "Initial Administrator Account Already Set Up". This happens for any page, eg. http://machine.domain:7080/arcgis/home/webmap/viewer.html The security "HTTPS only" option is false. Everything works ok if accessing only through 7443. I also tried installing the webadaptor, but when I try to access http://machine.domain/wa/home it switches again.