[Python] Backtrader Double Bollinger Band Error reg. Index out of Range

I'm trying to code a double bollinger bands strategy with Backtrader and get following error.

'''Starting Portfolio Value: 25000.00
---------------------------------------------------------------------------
IndexError Traceback (most recent call last)
<ipython-input-32-ddca45cee090> in <cell line: 2>()
1 print('Starting Portfolio Value: %.2f' % cerebro.broker.getvalue())
----> 2 cerebro.run()
3 print('Final Portfolio Value: %.2f' % cerebro.broker.getvalue())

6 frames
/usr/local/lib/python3.10/dist-packages/backtrader/linebuffer.py in __getitem__(self, ago)
161
162 def __getitem__(self, ago):
--> 163 return self.array[self.idx + ago]
164
165 def get(self, ago=0, size=1):

IndexError: array index out of range
'''


Here is the code I have. The issue I think is from the line 'Buy Condition 1', looking into the past 4 periods. Does it have something to do with setting up the data? How can I fix this? Thank you for your time in advance!!

'''data = bt.feeds.YahooFinanceCSVData(
dataname = 'BTC_22-24_4H.csv', openinterest = 6
)

cerebro = bt.Cerebro()
cerebro.adddata(data)
class DoubleBB(bt.Strategy):
params = (
('bb_period', 20),
('dev1', 1),
('dev2', 2)
)

def __init__(self):
# Bollinger band with deviation 1
self.bb1 = bt.ind.BollingerBands(period=self.params.bb_period, devfactor=self.params.dev1)
#Bollinger band with deviation 2
self.bb2 = bt.ind.BollingerBands(period=self.params.bb_period, devfactor=self.params.dev2)

# Buy Condition 1: In the last 4 periods, at least one low price was below the lower band of bb2
self.low_below_bb2 = any(self.data.low[-i] <= self.bb2.bot[-i] for i in range(1, 4))
# Buy Condition 2: Previous close price crosses over the lower band of bb1
self.bb1_lower = bt.indicators.CrossOver(self.data.close, self.bb1.lines.bot, plotname='buy sig')
# Buy Condition 3: Previous close price is between the lower band of bb1 and the middle line

# Exit Condition 1: Close price crosses below the upper band of bb1
self.bb1_upper = bt.indicators.CrossOver(self.data.close, self.bb1.lines.top, plotname='sell sig')

def next(self):

if not self.position:
if (self.bb1_lower > 0) and low_below_bb2:
self.buy()
else:
if self.bb1_upper < 0:
self.close()
'''

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