As promised, I've filed FB25244212 with a sysdiagnose from an affected customer's iPhone (iOS 27.0.1, 24A446). It was taken about a minute after a restart, before our app was opened, and the fonts were already gone from Settings > General > Fonts. The report references FB25170142, which has the sample project.

Thanks for confirming. I've filed FB25170142 with a sample project. It registers a font with kCTFontManagerScopePersistent and shows the registered list next to UIFont(name:size:), so the mismatch after a reboot is easy to see. It also covers the 105 error and the unregister-then-register fix. We're collecting sysdiagnose files from affected customers and will send them in a separate report referencing FB25170142.

Thanks for confirming. I've filed FB25170142 with a sample project. It registers a font with kCTFontManagerScopePersistent and shows the registered list next to UIFont(name:size:), so the mismatch after a reboot is easy to see. It also covers the 105 error and the unregister-then-register fix. We're collecting sysdiagnose files from affected customers and will send them in a separate report referencing FB25170142.