I'm using Zorro S 2.62.1 with a master script launching two backtests via zOpen() (Core 2 and 3).

Both child processes have LOGFILE enabled and a nonzero LogNumber. Reports and trade CSVs are generated correctly, but the native _pnl.csv and _pnl.dbl files are missing.

Running the exact same script directly (Core 1), even with zInit(), generates both PnL files correctly.

Is this expected behavior for zOpen() child processes, or is there a way to enable native PnL export?

There ís no difference between a master or child process regarding exported files, but make sure that they have different names. Either use different named scripts, or set the name with the LogNumber or RootName variables.