diff --git a/piker/data/history.py b/piker/data/history.py
index eea6e83f..fce81063 100644
--- a/piker/data/history.py
+++ b/piker/data/history.py
@@ -19,9 +19,9 @@ Historical data business logic for load, backfill and tsdb storage.
 
 '''
 from __future__ import annotations
-from collections import (
-    Counter,
-)
+# from collections import (
+#     Counter,
+# )
 from datetime import datetime
 from functools import partial
 # import time
@@ -86,6 +86,7 @@ def diff_history(
     else:
         return array[times >= prepend_until_dt.timestamp()]
 
+
 async def shm_push_in_between(
     shm: ShmArray,
     to_push: np.ndarray,
@@ -191,7 +192,7 @@ async def start_backfill(
         # avoid duplicate history frames with a set of datetime frame
         # starts and associated counts of how many duplicates we see
         # per time stamp.
-        starts: Counter[datetime] = Counter()
+        # starts: Counter[datetime] = Counter()
 
         # conduct "backward history gap filling" where we push to
         # the shm buffer until we have history back until the
@@ -201,11 +202,6 @@ async def start_backfill(
 
         while last_start_dt > backfill_until_dt:
 
-            # if timeframe == 60:
-            #     await tractor.breakpoint()
-            # else:
-            #     return
-
             log.debug(
                 f'Requesting {timeframe}s frame ending in {last_start_dt}'
             )
@@ -242,6 +238,7 @@ async def start_backfill(
             #         f"{mkt.fqme}: skipping duplicate frame @ {next_start_dt}"
             #     )
             #     starts[start_dt] += 1
+            #     await tractor.breakpoint()
             #     continue
 
             # elif starts[next_start_dt] > 6:
@@ -250,13 +247,12 @@ async def start_backfill(
             #     )
             #     return
 
-            # only update new start point if not-yet-seen
-            start_dt: datetime = next_start_dt
-            starts[start_dt] += 1
+            # # only update new start point if not-yet-seen
+            # starts[next_start_dt] += 1
 
-            assert array['time'][0] == start_dt.timestamp()
+            assert array['time'][0] == next_start_dt.timestamp()
 
-            diff = last_start_dt - start_dt
+            diff = last_start_dt - next_start_dt
             frame_time_diff_s = diff.seconds
 
             # frame's worth of sample-period-steps, in seconds
@@ -279,11 +275,12 @@ async def start_backfill(
             )
             ln = len(to_push)
             if ln:
-                log.info(f'{ln} bars for {start_dt} -> {last_start_dt}')
+                log.info(f'{ln} bars for {next_start_dt} -> {last_start_dt}')
 
             else:
                 log.warning(
-                    f'{ln} BARS TO PUSH after diff?!: {start_dt} -> {last_start_dt}'
+                    '0 BARS TO PUSH after diff!?\n'
+                    f'{next_start_dt} -> {last_start_dt}'
                 )
 
             # bail gracefully on shm allocation overrun/full
@@ -308,7 +305,7 @@ async def start_backfill(
             except ValueError as ve:
                 _ve = ve
                 log.error(
-                    f'Shm buffer prepend OVERRUN on: {start_dt} -> {last_start_dt}?'
+                    f'Shm prepend OVERRUN on: {next_start_dt} -> {last_start_dt}?'
                 )
 
                 if next_prepend_index < ln:
@@ -336,7 +333,7 @@ async def start_backfill(
 
             log.info(
                 f'Shm pushed {ln} frame:\n'
-                f'{start_dt} -> {last_start_dt}'
+                f'{next_start_dt} -> {last_start_dt}'
             )
 
             # FINALLY, maybe write immediately to the tsdb backend for
@@ -347,7 +344,7 @@ async def start_backfill(
             ):
                 log.info(
                     f'Writing {ln} frame to storage:\n'
-                    f'{start_dt} -> {last_start_dt}'
+                    f'{next_start_dt} -> {last_start_dt}'
                 )
 
                 if mkt.dst.atype not in {'crypto', 'crypto_currency'}:
@@ -372,50 +369,52 @@ async def start_backfill(
                 f'Finished filling gap to tsdb start @ {backfill_until_dt}!'
             )
             # conduct tsdb timestamp gap detection and backfill any
-            # seemingly missing portions!
-
+            # seemingly missing sequence segments..
+            # TODO: ideally these never exist but somehow it seems
+            # sometimes we're writing zero-ed segments on certain
+            # (teardown) cases?
             from ._timeseries import detect_null_time_gap
 
-            indices: tuple | None = detect_null_time_gap(shm)
-            if indices:
+            gap_indices: tuple | None = detect_null_time_gap(shm)
+            while gap_indices:
                 (
                     istart,
                     start,
                     end,
                     iend,
-                ) = indices
+                ) = gap_indices
+
+                start_dt = from_timestamp(start)
+                end_dt = from_timestamp(end)
                 (
                     array,
                     next_start_dt,
                     next_end_dt,
                 ) = await get_hist(
                     timeframe,
-                    start_dt=from_timestamp(start),
-                    end_dt=from_timestamp(end),
+                    start_dt=start_dt,
+                    end_dt=end_dt,
                 )
+
                 await shm_push_in_between(
                     shm,
                     array,
                     prepend_index=iend,
                     update_start_on_prepend=False,
                 )
+
+                # TODO: UI side needs IPC event to update..
+                # - make sure the UI actually always handles
+                #  this update!
+                # - remember that in the display side, only refersh this
+                #   if the respective history is actually "in view".
+                #   loop
                 await sampler_stream.send({
                     'broadcast_all': {
                         'backfilling': True
                     },
                 })
-            indices: tuple | None = detect_null_time_gap(shm)
-            if indices:
-                (
-                    istart,
-                    start,
-                    end,
-                    iend,
-                ) = indices
-                await tractor.breakpoint()
-
-        # TODO: can we only trigger this if the respective
-        # history in "in view"?!?
+                gap_indices: tuple | None = detect_null_time_gap(shm)
 
         # XXX: extremely important, there can be no checkpoints
         # in the block above to avoid entering new ``frames``