Hi there! I understand that you're having trouble with some pictures not showing in the Flipped app on your Mac running OS X 10.15.7. To help you better, could you tell me a bit more about when this started happening? Are the missing pictures ones you uploaded recently, or are some older ones not showing? Also, is the problem with all photos in the app or just specific ones? Any extra detail will help me guide you more precisely.

Meanwhile, here are some initial steps we can try to resolve missing photos in the app:

1. Check Internet Connection: Some photos might not load if your connection is unstable. Make sure your Mac is connected to a reliable Wi-Fi network.

2. Restart the Flipped App: Quit the app completely and restart it. This often helps refresh the content display.

3. Update the Flipped App: Ensure you have the latest version of Flipped installed from the Mac App Store. Updates often fix bugs that could cause photos to disappear.

4. Check App Permissions: On your Mac, go to System Preferences > Security & Privacy > Privacy tab, then check if Flipped has permission to access Photos. Sometimes, if permission is revoked or not granted, photos may not display properly.

5. Free Up Space: If your Mac is low on storage, the app may struggle to cache images properly. Check your available disk space under About This Mac > Storage.

If you’ve already tried any of these, let me know which ones so I can suggest some deeper troubleshooting or other solutions. Does this make sense so far?