Hi! I tried to make a simple momentum strategy - buy best ETF if returns are positive for lookback period, rebalance monthly. I'm confused by the return function. Contrary to the size of the lookback period (63 days), I get a data interval (closing_bars) of 44, 43, 42 days. What am I doing wrong? Why are these numbers changing!?Where to read about how to warm up the algorithm correctly? I thought I did everything right, but I got an error

Thanks in advance for your help,

Ilya