Solved
Is the "Creo Performance Advisor" offline?
For some days now it's impossible for me to open the web interface of the "Creo Performance Advisor".
Is it offline and if yes, when will it be available again?
Yes, it appears to still be down. See this post here: https://community.ptc.com/t5/PTC-eSupport-Help/July-2017-Web-Release/gpm-p/478072#M325