I have written a strategy that relies on a 200-day SMA. Therefore, during the first 200 days in my strategy, this indicator simply is not available.
How can I make it that backtrader only runs my strategy once it has gathered the data for 200 days so that my SMA 200 indicator is available?

I have written a simple Python script using backtrader that is supposed to sell an ETF (SPY in my case) when the price of the ETF is over its 200-day simple moving average (SMA200). The code is as follows:

import backtrader as bt
import yfinance

stock = yfinance.Ticker("SPY")
stock_data = stock.history(period="4y")

# print(stock_data.head())


class SMA200Strategy(bt.Strategy):
    def __init__(self):
        self.etf = self.datas[0]
        self.etf_sma = bt.ind.SMA(self.etf.lines.close, period=200)
        self.crossover = bt.ind.CrossOver(self.etf, self.etf_sma)

    def next(self):
        if self.crossover > 0:
            self.order_target_percent(self.etf, target=1)
        elif self.crossover < 0:
            self.order_target_percent(self.etf, target=0)


cerebro = bt.Cerebro()

cerebro.broker.setcash(100000)
cerebro.adddata(
    bt.feeds.PandasData(dataname=stock_data))
cerebro.addstrategy(SMA200Strategy)

cerebro.run()
cerebro.plot()

The crossover occurs at the correct points, however, backtrader doesnt execute my sell/buy command (self.order_target_percent(self.etf, target=1)/self.order_target_percent(self.etf, target=0))

You can see in this image outputted by backtrader that the crossover signals are generated, but then no buy/sell orders are executed in many cases: Imgur

I have tried using other data but I checked and the data loaded by yfinance is correct and in the fitting format (a pandas dataframe).

I have also tried self.buy and self.close, but even those commands don´t work reliably.

How can I make backtrader actually execute my buy/sell commands in all cases?