This has been happening to me as well. I have 7 apps. Everything was fine and then last week, all apps (builds) were removed from TestFlight. No explanation, just gone. Each new build I upload now shows in TestFlight but I cannot install any of them: “The requested app is not available or doesn't exist”. I have attempted to contact Apple through the “unhelpful” portal but no response. i have tried calling various Apple support lines but they all tell me there is nothing they can do. I need to contact Apple Developer Support. They dont have a number, It must be done through the portal. Super Frustrating!