I used the "Search" (Upper right corner at the menu bar) in Discussion

Thank you for bringing this to our attention. Appian is working on this issue and we expect the search to be working fine again soon. You should still be able no navigate to the documentation and search within the docs from that search box or use Tempo in the meantime. These tools won't search within discussions but are also good sources of information.

Eduardo Fuentes
Appian Technical Support

This is working again.

Thanks for your effort!