I’d try a build from scratch. Something may have gotten corrupted.
You can do this by closing the editor, deleting all the intermediate directories in your project root, and rebuilding the project. You want to delete “Binaries”, “Build”, “Intermediate”, “Saved”, and “DerivedDataCache”. If you are using C++ then you will need to right-click your uproject file and generate project files again (don’t delete the “vs” directory or VS will have to rebuild its database). If you are using any plugins, delete the intermediate directories for each of those as well.