Why does copy_rates_range() return only 1 or 0 bar most of the time in MetaTrader5?

I am using MetaTrader 5 for python and regardless of the specified range, symbol and timeframe, copy_rates_range() almost always returns 0 or 1 bars. In the docs they say it's normal for the first call and that the requested data will be ready for subsequent calls but it just never is.