diff --git a/piker/data/feed.py b/piker/data/feed.py
index 1843b302..e4f4844a 100644
--- a/piker/data/feed.py
+++ b/piker/data/feed.py
@@ -25,6 +25,7 @@ from dataclasses import dataclass, field
 from datetime import datetime
 from contextlib import asynccontextmanager
 from functools import partial
+from pprint import pformat
 from types import ModuleType
 from typing import (
     Any,
@@ -322,7 +323,8 @@ async def start_backfill(
                     start,
                     last_tsdb_dt,
                 )
-                dtrange = hist_period.range('seconds', frame_size_s)
+                dtrange = list(hist_period.range('seconds', frame_size_s))
+                log.debug(f'New datetime index:\n{pformat(dtrange)}')
 
                 for end_dt in dtrange:
                     log.warning(f'Yielding next frame start {end_dt}')
@@ -395,7 +397,7 @@ async def start_backfill(
 
             diff = end_dt - start_dt
             frame_time_diff_s = diff.seconds
-            expected_frame_size_s = frame_size_s + step_size_s
+            expected_frame_size_s = frame_size_s  # + step_size_s
 
             if frame_time_diff_s > expected_frame_size_s:
 
@@ -515,27 +517,40 @@ async def start_backfill(
 
                 epochs = list(reversed(sorted(frames)))
                 for epoch in epochs:
+
                     start = shm.array['time'][0]
+                    last_shm_prepend_dt = pendulum.from_timestamp(start)
+                    earliest_frame_queue_dt = pendulum.from_timestamp(epoch)
 
                     diff = epoch - start
                     if abs(diff) > step_size_s:
 
-                        if earliest_end_dt < end_dt:
+                        if earliest_end_dt < earliest_frame_queue_dt:
                             # XXX: an expected gap was encountered (see
                             # logic in ``get_ohlc_frame()``, so allow
                             # this frame through to the storage layer.
                             log.warning(
-                                f'there is an expected history gap of {diff}s:'
+                                f'Expected history gap of {diff}s:\n'
+                                f'{earliest_frame_queue_dt} <- '
+                                f'{earliest_end_dt}'
                             )
 
                         elif (
                             erlangs > 1
-                            and len(epochs) < erlangs
                         ):
                             # we don't yet have the next frame to push
                             # so break back to the async request loop
                             # while we wait for more async frame-results
                             # to arrive.
+                            if len(frames) >= erlangs:
+                                log.warning(
+                                    'Frame count in async-queue is greater '
+                                    'then erlangs?\n'
+                                    'There seems to be a gap between:\n'
+                                    f'{earliest_frame_queue_dt} <- '
+                                    f'{last_shm_prepend_dt}'
+                                )
+
                             expect_end = pendulum.from_timestamp(start)
                             expect_start = expect_end.subtract(
                                 seconds=frame_size_s)