1.8.6+ needs a limit on number of parallel builds it will fork for small memory systems. A safe default would be number of cores present, with an option to select single-threaded for folks who don' t mind waiting. https://forum.arduino.cc/index.php?topic=603700.0 Cheers!

Limit parallel builds forked by IDE

pert August 23, 2019, 11:19am 14

A related issue was recently opened on GitHub and an investigation was done by one of the Arduino developers:

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