Ok, well... the iOS update wasn't the answer. Yesterday, the problem came back. It was at the end of my work day, so I just power cycled the iPad and left it alone overnight. This morning, it start working again ¯\_(ツ)_/¯

I had this error show up today, despite the same app working fine yesterday. The only difference, was that this morning macOS 11.3.1 and iOS 14.5.1 were released to fix a security issue with (I think?) Safari. I had updated macOS to 11.3.1, but my iPad was still on 14.5. After updating my iPad to 14.5.1, and doing all the normal Xcode stuff like clearing derived data and cleaning the build folder (for the umpteenth time!), it started working again. I have no idea if updating iOS fixed it or not, but if you can, it's worth a shot? I'm also not entire sure about the device blocking the app... how can you tell if it is?