Answer
Users with no explicit home-page configuration default to IFS's own standard 'Welcome' Lobby (a fixed, specific page) — but that standard Welcome Lobby isn't granted to any standard permission set by default, so on a genuinely fresh permission-set structure, every user hits this 'data not found' error immediately on login before you've even gotten to configuring your own custom lobbies. Fix it by granting that specific Welcome Lobby's presentation object: in Permission Set > Presentation Objects by Component, search using a % prefix followed by the Welcome Lobby's page-id GUID (b712d6d1-fe57-4d51-a7e0-8c3a6b1f4ce7), and grant it. If a different, specific lobby is actually meant to be the user's real home page instead, set that explicitly via Options > Home Page Address, using the address format ifswin:Ifs.Fnd.CompositePageRenderer.PageContainer?page_id=<LOBBY_PAGE_ID>.