EDIT: This appears to be fixed now. Re-download FW 2.4 archive with the updated iOS ANE inside. Thanks Jake, Jon & others for providing details!
There’s a bug in the 2.4 release – it is most likely connected to saveToGallery on iOS and demonstrates itself as a crash just after stopping the recording. We know about the issue and are working to fix this asap. As a workaround try to use saving to gallery with empty arguments, which won’t attemp to use albums (the likely cause of the crash):