I really have an issue when it's about syncing Lighroom on my iPhone, Lighroom on my iMac and the web version. Why does Lighroom on my iMac not show the same amount of pictures as on my iPhone? And when I open the web version which is called something "syncing errors" ("Synchronisierungsfehler" in German). The number of pictures there are in my opinion exactly the one that are missing in Lighroom on my iMac. On my iPhone Lighroom automatically adds the photos made with the native photos app and the one I'm taking with the lightroom app.
How can I make sure that I see everywhere the same pictures?
Assuming that the photos with the issues are coming from the iPhone, can you identify the photos in Lightroom Web that are having the issues?
Once identified, trying perform some minor edits to the photos in Lightroom on the iPhone sometimes can kick start the sync apparently. After the see if the sync completes by checking the Cloud icon within the app.