diff --git a/CliClient/run_test.sh b/CliClient/run_test.sh
index 4af0b35e0..17794306e 100755
--- a/CliClient/run_test.sh
+++ b/CliClient/run_test.sh
@@ -10,7 +10,7 @@ rsync -a "$ROOT_DIR/../ReactNativeClient/locales/" "$BUILD_DIR/locales/"
 mkdir -p "$BUILD_DIR/data"
 
 if [[ $TEST_FILE != "" ]]; then
-	(cd "$ROOT_DIR" && npm test tests-build/$TEST_FILE.js)
+	(cd "$ROOT_DIR" && NODE_ENV=testing npm test tests-build/$TEST_FILE.js)
 	exit
 fi
 
@@ -21,27 +21,27 @@ function finish {
 trap finish EXIT
 
 cd "$ROOT_DIR"
-npm test tests-build/ArrayUtils.js && \
-npm test tests-build/encryption.js && \
-npm test tests-build/EnexToMd.js && \
-npm test tests-build/HtmlToMd.js && \
-npm test tests-build/markdownUtils.js && \
-npm test tests-build/models_BaseItem.js && \
-npm test tests-build/models_Folder.js && \
-npm test tests-build/models_ItemChange.js && \
-npm test tests-build/models_Note.js && \
-npm test tests-build/models_Resource.js && \
-npm test tests-build/models_Revision.js && \
-npm test tests-build/models_Setting.js && \
-npm test tests-build/models_Tag.js && \
-npm test tests-build/pathUtils.js && \
-npm test tests-build/services_InteropService.js && \
-npm test tests-build/services_KvStore.js && \
-npm test tests-build/services_ResourceService.js && \
-npm test tests-build/services_rest_Api.js && \
-npm test tests-build/services_SearchEngine.js && \
-npm test tests-build/services_Revision.js && \
-npm test tests-build/StringUtils.js && \
-npm test tests-build/TaskQueue.js && \
-npm test tests-build/synchronizer.js && \
-npm test tests-build/urlUtils.js
\ No newline at end of file
+NODE_ENV=testing npm test tests-build/ArrayUtils.js && \
+NODE_ENV=testing npm test tests-build/encryption.js && \
+NODE_ENV=testing npm test tests-build/EnexToMd.js && \
+NODE_ENV=testing npm test tests-build/HtmlToMd.js && \
+NODE_ENV=testing npm test tests-build/markdownUtils.js && \
+NODE_ENV=testing npm test tests-build/models_BaseItem.js && \
+NODE_ENV=testing npm test tests-build/models_Folder.js && \
+NODE_ENV=testing npm test tests-build/models_ItemChange.js && \
+NODE_ENV=testing npm test tests-build/models_Note.js && \
+NODE_ENV=testing npm test tests-build/models_Resource.js && \
+NODE_ENV=testing npm test tests-build/models_Revision.js && \
+NODE_ENV=testing npm test tests-build/models_Setting.js && \
+NODE_ENV=testing npm test tests-build/models_Tag.js && \
+NODE_ENV=testing npm test tests-build/pathUtils.js && \
+NODE_ENV=testing npm test tests-build/services_InteropService.js && \
+NODE_ENV=testing npm test tests-build/services_KvStore.js && \
+NODE_ENV=testing npm test tests-build/services_ResourceService.js && \
+NODE_ENV=testing npm test tests-build/services_rest_Api.js && \
+NODE_ENV=testing npm test tests-build/services_SearchEngine.js && \
+NODE_ENV=testing npm test tests-build/services_Revision.js && \
+NODE_ENV=testing npm test tests-build/StringUtils.js && \
+NODE_ENV=testing npm test tests-build/TaskQueue.js && \
+NODE_ENV=testing npm test tests-build/synchronizer.js && \
+NODE_ENV=testing npm test tests-build/urlUtils.js
\ No newline at end of file
diff --git a/CliClient/tests/synchronizer.js b/CliClient/tests/synchronizer.js
index 3758b8029..707208d78 100644
--- a/CliClient/tests/synchronizer.js
+++ b/CliClient/tests/synchronizer.js
@@ -1481,19 +1481,27 @@ describe('Synchronizer', function() {
 	}));
 
 	it('should not wipe out user data when syncing with an empty target', asyncTest(async () => {
-		await Note.save({ title: 'ma note' });
-		await Note.save({ title: 'mon autre note' });
-		await Note.save({ title: 'ma troisième note' });
+		for (let i = 0; i < 10; i++) await Note.save({ title: 'note' });
 
 		Setting.setValue('sync.wipeOutFailSafe', true);
 		await synchronizer().start();
 		await fileApi().clearRoot(); // oops
 		await synchronizer().start();
-		expect((await Note.all()).length).toBe(3); // but since the fail-safe if on, the notes have not been deleted
+		expect((await Note.all()).length).toBe(10); // but since the fail-safe if on, the notes have not been deleted
 
 		Setting.setValue('sync.wipeOutFailSafe', false); // Now switch it off
 		await synchronizer().start();
 		expect((await Note.all()).length).toBe(0); // Since the fail-safe was off, the data has been cleared
+
+		// Handle case where the sync target has been wiped out, then the user creates one note and sync.
+
+		for (let i = 0; i < 10; i++) await Note.save({ title: 'note' });
+		Setting.setValue('sync.wipeOutFailSafe', true);
+		await synchronizer().start();
+		await fileApi().clearRoot();
+		await Note.save({ title: 'ma note encore' });
+		await synchronizer().start();
+		expect((await Note.all()).length).toBe(11);
 	}));
 
 });
diff --git a/ReactNativeClient/lib/file-api.js b/ReactNativeClient/lib/file-api.js
index 52d9ac51e..34a83821e 100644
--- a/ReactNativeClient/lib/file-api.js
+++ b/ReactNativeClient/lib/file-api.js
@@ -5,6 +5,7 @@ const BaseItem = require('lib/models/BaseItem.js');
 const JoplinError = require('lib/JoplinError');
 const ArrayUtils = require('lib/ArrayUtils');
 const { time } = require('lib/time-utils.js');
+const { sprintf } = require('sprintf-js');
 
 function requestCanBeRepeated(error) {
 	const errorCode = typeof error === 'object' && error.code ? error.code : null;
@@ -262,13 +263,6 @@ async function basicDelta(path, getDirStatFn, options) {
 		});
 		newContext.statIdsCache = newContext.statsCache.filter(item => BaseItem.isSystemPath(item.path)).map(item => BaseItem.pathToId(item.path));
 		newContext.statIdsCache.sort(); // Items must be sorted to use binary search below
-
-		// At this point statIdsCache contains the list of all the item IDs on the sync target.
-		// If it's empty, it's most likely a configuration error or bug. For example, if the
-		// user moves their Nextcloud directory, or if a network drive gets disconnected and
-		// returns an empty dir instead of an error. In that case, we don't wipe out the user
-		// data, unless they have switched off the fail-safe.
-		if (options.wipeOutFailSafe && !newContext.statIdsCache.length) throw new JoplinError('Fail-safe: The delta operation was interrupted because the sync target appears to be empty. To override this behaviour disable the "Wipe out fail-safe" option in the settings.', 'failSafe');
 	}
 
 	let output = [];
@@ -322,6 +316,15 @@ async function basicDelta(path, getDirStatFn, options) {
 			}
 		}
 
+		const percentDeleted = itemIds.length ? deletedItems.length / itemIds.length : 0;
+
+		// If more than 90% of the notes are going to be deleted, it's most likely a
+		// configuration error or bug. For example, if the user moves their Nextcloud
+		// directory, or if a network drive gets disconnected and returns an empty dir
+		// instead of an error. In that case, we don't wipe out the user data, unless
+		// they have switched off the fail-safe.
+		if (options.wipeOutFailSafe && percentDeleted >= 0.90) throw new JoplinError(sprintf('Fail-safe: Sync was interrupted because %d%% of the data (%d items) is about to be deleted. To override this behaviour disable the fail-safe in the sync settings.', Math.round(percentDeleted * 100), deletedItems.length), 'failSafe');
+
 		output = output.concat(deletedItems);
 	}
 
diff --git a/ReactNativeClient/lib/shim-init-node.js b/ReactNativeClient/lib/shim-init-node.js
index de268fb20..87f040ad6 100644
--- a/ReactNativeClient/lib/shim-init-node.js
+++ b/ReactNativeClient/lib/shim-init-node.js
@@ -362,6 +362,10 @@ function shimInit() {
 		bridge().openExternal(url);
 	};
 
+	shim.isTestingEnv = () => {
+		return process.env.NODE_ENV === 'testing';
+	};
+
 	shim.waitForFrame = () => {};
 }
 
diff --git a/ReactNativeClient/lib/shim.js b/ReactNativeClient/lib/shim.js
index 8cde2e3d5..f39bcb31e 100644
--- a/ReactNativeClient/lib/shim.js
+++ b/ReactNativeClient/lib/shim.js
@@ -198,4 +198,8 @@ shim.loadCssFromJs = name => {
 	throw new Error('Not implemented');
 };
 
+shim.isTestingEnv = () => {
+	return false;
+};
+
 module.exports = { shim };
diff --git a/ReactNativeClient/lib/synchronizer.js b/ReactNativeClient/lib/synchronizer.js
index 1b4bd9c6e..2dde431ad 100644
--- a/ReactNativeClient/lib/synchronizer.js
+++ b/ReactNativeClient/lib/synchronizer.js
@@ -715,7 +715,11 @@ class Synchronizer {
 				// Or it's a temporary issue that will be resolved on next sync.
 				this.logger().info(error.message);
 
-				if (error.code === 'failSafe') this.logLastRequests();
+				if (error.code === 'failSafe') {
+					// Get the message to display on UI, but not in testing to avoid poluting stdout
+					if (!shim.isTestingEnv()) this.progressReport_.errors.push(error.message);
+					this.logLastRequests();
+				}
 			} else if (error.code === 'unknownItemType') {
 				this.progressReport_.errors.push(_('Unknown item type downloaded - please upgrade Joplin to the latest version'));
 				this.logger().error(error);