I've just downloaded version 27.4.4 and when editing a page using the "Edit" option (1 on attached figure), I get an 404 error (2 on figure). Item 3 on figure shows the system vars.
When creating a new file, I can edit just fine (item 4 on figure); but once the file is saved and I try to edit it, the 404 error shows again. The "Edit with Bebuilder" option works fine.