It will probably be too brief for us to even realize, but I thought I'd mention it here.Planned outage Search performance, and page loads for book landing pages, has been problematic. There will be a brief outage on Thursday April 29 to transition to an upgraded database server, as part of the effort to improve performance.
Also on gutenberg's homepage:
Planned service change In April 2021, www.gutenberg.org plans to remove unencrypted access (http), and will only offer https. The collection remains available from mirrors, as well as via unencrypted ftp and rsync.