After observing some weirdness in backfilling LookBack data from MT4, I found out that Zorro does not always request M1 bars.

For BarPeriod=60 it requests 15min bars, for BarPeriod = 30 - 5min bars.

This does not work if BarOffset is set (which I believe was the reason to request M1 bars by default).

This is since v 2.28.xx....probably also 2.27.xx...earlier versions requested PERIOD_M1 historical candles from MT4.