Realm data not visible for Client Java SDK

I have setup a Realm App and Atlas database correctly. I activated device sync and developer mode and put read and write access to just “true”. I added some documents to some collections with MongoDB Compass.
Now I try to connect in Android Studio with Java SDK via a user email and password (that I created in the Realm UI). The user gets logged in. Then I initialize Realm etc. and it works. Then I try a symple query on the realm and no data at all gets found. No error, just no data there. It behaves as if the entire realm was empty. I also have Client Reset strategy like this, but it didn’t help. The client just does not get ANY data.

                        @Override
                        public void onBeforeReset(Realm realm) {
                            Log.w("auth", "Beginning client reset for " + realm.getPath());
                        }
                        @Override
                        public void onAfterReset(Realm before, Realm after) {
                            Log.w("auth", "Finished client reset for " + before.getPath());
                        }
                        @Override
                        public void onError(SyncSession session, ClientResetRequiredError error) {
                            Log.e("auth", "Couldn't handle the client reset automatically." +
                                    " Falling back to manual client reset execution: "
                                    + error.getErrorMessage());
                            // close all instances of your realm -- this application only uses one
                            dbApp..close();
                            try {
                                Log.w("auth", "About to execute the client reset.");
                                // execute the client reset, moving the current realm to a backup file
                                error.executeClientReset();
                                Log.w("auth", "Executed the client reset.");
                            } catch (IllegalStateException e) {
                                Log.e("auth", "Failed to execute the client reset: " + e.getMessage());
                                // The client reset can only proceed if there are no open realms.
                                // if execution failed, ask the user to restart the app, and we'll client reset
                                // when we first open the app connection.
                                Log.e("auth", "Sync error. Restart the application to resume sync.");
                            }
                            // open a new instance of the realm. This initializes a new file for the new realm
                            // and downloads the backend state. Do this in a background thread so we can wait
                            // for server changes to fully download.
                            ExecutorService executor = Executors.newSingleThreadExecutor();
                            executor.execute(() -> {
                                Realm newRealm = Realm.getDefaultInstance();
                                // ensure that the backend state is fully downloaded before proceeding
                                /*try {
                                    dbApp.getSync().getSession(globalConfig).downloadAllServerChanges(10000,
                                            TimeUnit.MILLISECONDS);
                                } catch (InterruptedException e) {
                                    e.printStackTrace();
                                }*/
                                Log.w("auth","Downloaded server changes for a fresh instance of the realm.");
                                newRealm.close();
                            });
                            // execute the recovery logic on a background thread
                            try {
                                executor.awaitTermination(20000, TimeUnit.MILLISECONDS);
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }
                        }
                    })

The client reset also works but still, I don’t get any data.