diff --git a/src/main/java/eu/openaire/urls_controller/util/FileUtils.java b/src/main/java/eu/openaire/urls_controller/util/FileUtils.java
index f7196bb..7e2eba1 100644
--- a/src/main/java/eu/openaire/urls_controller/util/FileUtils.java
+++ b/src/main/java/eu/openaire/urls_controller/util/FileUtils.java
@@ -290,7 +290,7 @@ public class FileUtils {
                     continue;   // To the next batch.
                 }
                 else if ( (extractedFileNames.length -2) != fileNamesForCurBatch.size() ) {
-                    logger.warn("The number of extracted files (" + (extractedFileNames.length -2) + ") was not equal to the number of the current-batch's files (" + fileNamesForCurBatch.size() + ").");
+                    logger.warn("The number of extracted files (" + (extractedFileNames.length -2) + ") was not equal to the number of the current-batch's (" + batchCounter + ") files (" + fileNamesForCurBatch.size() + ").");
                     // We do NOT have to find and cross-reference the missing files with the urlReports, in order to set their locations to <null>,
                     // since, in the end of each assignments-batch, an iteration will be made and for all the non-retrieved and non-uploaded full-texts, the app will set them to null.
                 }
@@ -330,9 +330,13 @@ public class FileUtils {
             conn.connect();
             int statusCode = conn.getResponseCode();
             if ( statusCode != 200 ) {
-                logger.warn("HTTP-" + statusCode + ": " + getMessageFromResponseBody(conn, true) + "\nProblem when requesting the ZstdFile of batch_" + batchNum + " from the Worker with ID \"" + workerId + "\" and requestUrl: " + requestUrl);
+                logger.warn("HTTP-" + statusCode + ": " + getMessageFromResponseBody(conn, true) + "\n\nProblem when requesting the ZstdFile of batch_" + batchNum + " from the Worker with ID \"" + workerId + "\" and requestUrl: " + requestUrl);
+                if ( (statusCode >= 500) && (statusCode <= 599) )
+                    throw new RuntimeException();   // Throw an exception to indicate that the Worker has problems and all remaining batches will fail as well.
                 return null;
             }
+        } catch (RuntimeException re) {
+            throw re;
         } catch (Exception e) {
             String exMessage = e.getMessage();
             logger.warn("Problem when requesting the ZstdFile of batch_" + batchNum + " of assignments_" + assignmentsBatchCounter + " from the Worker with ID \"" + workerId + "\" and requestUrl: " + requestUrl + "\n" + exMessage);
@@ -413,6 +417,16 @@ public class FileUtils {
                     continue;
                 }
 
+                if ( datasourceId == null ) {
+                    logger.error("The retrieved \"datasourceId\" was \"null\" for file: " + fileName);
+                    continue;
+                }
+
+                if   ( hash == null ) {
+                    logger.error("The retrieved \"hash\" was \"null\" for file: " + fileName);
+                    continue;
+                }
+
                 String fileFullPath = targetDirectory + fileName;   // The fullPath to the local file.
 
                 // Use the "fileNameID" and not the "filenameWithoutExtension", as we want to avoid keeping the possible "parenthesis" with the increasing number (about the duplication of ID-fileName).