Bug Animations' sprites go missing every time the project is reloaded

Hi. I'm working on a project in Unity, and I've found either a bug, or a really weird issue. Whenever I reload my project, my animations' sprites all go missing, and they don't display anymore. The sprites are all still in the exact same place on the hard drive, but the editor can't find them for whatever reason. This only started happening after I've upgraded the project to Unity 2019.4.1f1, which is the latest version, according to both the hub and the editor. I can't continue working on my game if I have to spend an increasing amount of time re-creating animations every time I reload the editor. Any help is appreciated.