Seems quite odd. It also happened to me today morning. After upgrading to iOS 14 Beta 3, the existing ipa with enterprise provisioning started not to be installed on the iOS 14 device, which was working fine on iOS 14 Beta 1.
After building the app with newer version of Xcode(11.4), the app is now working fine on iOS 14 Beta 3. The previous was built with iPhone os 10.3 sdk.