Regression from https://gerrit.wikimedia.org/r/#/c/308011/
When enabling Flow on a page that already exist, the existing page is moved to an archived and a template is added to it to specify that this is an archive and where the non-archive page can be found.
Now, the move seems to work but when we try to add the template we cannot find any revision at the expected location (e.g. Talk:User1/Archive_1)
See Flow/Import/Converter.php:281