diff --git a/modem/arq_session_irs.py b/modem/arq_session_irs.py
index 80d67ddb..32d9ecfd 100644
--- a/modem/arq_session_irs.py
+++ b/modem/arq_session_irs.py
@@ -141,8 +141,11 @@ class ARQSessionIRS(arq_session.ARQSession):
         return None, None
 
     def process_incoming_data(self, frame):
+        print(frame)
         if frame['offset'] != self.received_bytes:
-            self.log(f"Discarding data offset {frame['offset']} vs {self.received_bytes}")
+            # TODO: IF WE HAVE AN OFFSET BECAUSE OF A SPEED LEVEL CHANGE FOR EXAMPLE,
+            # TODO: WE HAVE TO DISCARD THE LAST BYTES, BUT NOT returning False!!
+            self.log(f"Discarding data offset {frame['offset']} vs {self.received_bytes}", isWarning=True)
             return False
 
         remaining_data_length = self.total_length - self.received_bytes
@@ -197,10 +200,7 @@ class ARQSessionIRS(arq_session.ARQSession):
         else:
 
             ack = self.frame_factory.build_arq_burst_ack(self.id,
-                                                         self.received_bytes,
                                                          self.speed_level,
-                                                         self.frames_per_burst,
-                                                         self.snr,
                                                          flag_final=True,
                                                          flag_checksum=False)
             self.transmit_frame(ack, mode=FREEDV_MODE.signalling)
diff --git a/modem/arq_session_iss.py b/modem/arq_session_iss.py
index de924ace..ebea54be 100644
--- a/modem/arq_session_iss.py
+++ b/modem/arq_session_iss.py
@@ -94,7 +94,9 @@ class ARQSessionISS(arq_session.ARQSession):
             if retries == 8 and isARQBurst and self.speed_level > 0:
                 self.log("SENDING IN FALLBACK SPEED LEVEL", isWarning=True)
                 self.speed_level = 0
-                self.send_data({'flag':{'ABORT': False, 'FINAL': False}, 'speed_level': self.speed_level})
+                print(f" CONFIRMED BYTES: {self.confirmed_bytes}")
+                self.send_data({'flag':{'ABORT': False, 'FINAL': False}, 'speed_level': self.speed_level}, fallback=True)
+
                 return
 
         self.set_state(ISS_State.FAILED)
@@ -149,7 +151,7 @@ class ARQSessionISS(arq_session.ARQSession):
 
         return None, None
 
-    def send_data(self, irs_frame):
+    def send_data(self, irs_frame, fallback=None):
         # update statistics
         self.update_histograms(self.confirmed_bytes, self.total_length)
 
@@ -160,10 +162,9 @@ class ARQSessionISS(arq_session.ARQSession):
         #    self.event_manager.send_arq_session_progress(
         #        True, self.id, self.dxcall, self.confirmed_bytes, self.total_length, self.state.name, statistics=self.calculate_session_statistics(self.confirmed_bytes, self.total_length))
 
-
         if self.expected_byte_offset > self.total_length:
             self.confirmed_bytes = self.total_length
-        else:
+        elif not fallback:
             self.confirmed_bytes = self.expected_byte_offset
         self.log(f"IRS confirmed {self.confirmed_bytes}/{self.total_length} bytes")
 
diff --git a/tests/test_arq_session.py b/tests/test_arq_session.py
index b6b1e6a0..36f85701 100644
--- a/tests/test_arq_session.py
+++ b/tests/test_arq_session.py
@@ -86,7 +86,7 @@ class TestARQSession(unittest.TestCase):
                                           cls.irs_modem)
         
         # Frame loss probability in %
-        cls.loss_probability = 30
+        cls.loss_probability = 0
 
         cls.channels_running = True
 
@@ -100,7 +100,7 @@ class TestARQSession(unittest.TestCase):
                     continue
 
                 frame_bytes = transmission['bytes']
-                frame_dispatcher.new_process_data(frame_bytes, None, len(frame_bytes), 10, 0)
+                frame_dispatcher.new_process_data(frame_bytes, None, len(frame_bytes), 5, 0)
             except queue.Empty:
                 continue
         self.logger.info(f"[{threading.current_thread().name}] Channel closed.")
@@ -155,7 +155,7 @@ class TestARQSession(unittest.TestCase):
         self.establishChannels()
         params = {
             'dxcall': "AA1AAA-1",
-            'data': base64.b64encode(np.random.bytes(1000)),
+            'data': base64.b64encode(np.random.bytes(10000)),
             'type': "raw_lzma"
         }
         cmd = ARQRawCommand(self.config, self.iss_state_manager, self.iss_event_queue, params)