I think you should file a bug report and talk to the author.

A quick look into the source showed that he is shelling out his calls, and this seems to collide with parallel processes. This might also explain the dependency on the shell...

Just a guess ... 🤷🏻‍♂️

In reply to Re^3: console output invisible after script exit by LanX
in thread console output invisible after script exit by adambot

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