Add warning when expected default-frame duration diff then rxed

piker/tsp/__init__.py

@@ -500,7 +500,6 @@ async def start_backfill(
             )
 
             assert time[-1] == next_end_dt.timestamp()
-
             expected_dur: Interval = last_start_dt - next_start_dt
 
             # frame's worth of sample-period-steps, in seconds
@@ -1011,7 +1010,15 @@ async def tsdb_backfill(
             ]|None = config.get('frame_types', None)
             if def_frame_durs:
                 def_frame_size: Duration = def_frame_durs[timeframe]
-                assert def_frame_size == calced_frame_size
+                if def_frame_size != calced_frame_size:
+                    log.warning(
+                        f'Provider {mod.name!r} frame diff then declared ?\n\n'
+                        f'fqme: {mkt.fqme}\n'
+                        f'def_frame_size: {def_frame_size}\n'
+                        f'calced_frame_size: {calced_frame_size}\n\n'
+
+                        f'=> possibly the frame contains a GAP ?\n'
+                    )
             else:
                 # use what we calced from first frame above.
                 def_frame_size = calced_frame_size