Can no longer skip to next/past event in playback

While in playback, the buttons to skip to the next motion event (or go back to the previous one) are dimmed. This used to work. Same behavior on Android or iOS. I have restarted the cameras (pair of C24’s) and reformatted the SD cards. Live video works fine as does simply watching any time during playback. I know events exist because lots of them are listed under the Events button as well as being sent in real-time alerts to my phone.