mixing timeframe indicators

[goldcar]

I use two resample datas for 3 timeframe Boll indicators. before coding ,I do read the help page:
https://www.backtrader.com/docu/mixing-timeframes/indicators-mixing-timeframes/
Forgive me that I dont really understand its thoery. Here is my code:

class AG2022(bt.Strategy):
  boll_mid1m = []
  boll_mid5m = []
  boll_mid30m = []
  bollrace = []
  
 def __init__(self):
        self.buy_order = None
        self.live_data = False
        self.dataclose = self.data0.close
        self.order = None
        self.boll_mid1m = btind.BollingerBands(self.data0, period=26).mid
        self.boll_mid5m = bt.indicators.BollingerBands(self.data1, period=26).mid()
        self.boll_mid30m = bt.indicators.BollingerBands(self.data2, period=26).mid()
        self.bollrace = self.boll_mid5m[0] / self.boll_mid30m[-2]

def next(self):
     print(self.boll_mid1m[0])       
     print(self.bollrace[0])
if __name__ == '__main__':
    cerebro = bt.Cerebro()
    store = CTPStore(ctp_setting)
    init_backfill = 1000 if is_trading_period() else 0
    stockkwargs = dict(
        # latethrough=False,
        timeframe=bt.TimeFrame.Ticks,
        num_init_backfill=1000,
        # init_backfill=0
    )
    _TICKER = "ag2206.SHFE"
    data = store.getdata(dataname=_TICKER, **stockkwargs)
    cerebro.adddata(data)
    cerebro.resampledata(data, timeframe=bt.TimeFrame.Minutes, compression=5)
    cerebro.resampledata(data, timeframe=bt.TimeFrame.Minutes, compression=30)
    cerebro.addstrategy(AG2022, store=store)
    cerebro.run()

the print(self.boll_mid1m[0]) is ok.
the print(self.bollrace[0]), sometimes generates error
return self.array[self.idx + ago]
IndexError: array index out of range

or just nothing at all, not going into "next" section.
I guess it could be backfill not enough problem , so I increase to 1000maximum from provider.
but the value is always "0"

anything wrong in my code? appreciated for your help.