I never managed to reproduce the Core Dump but I found this : https://github.com/pycom/pycom-micropython-sigfox/commit/3f690a5733d31ff938aad6219c498f7d1bf98346 A bug fix, the issue was not resolved in the version I used. This issue could explain the core dump I encountered. The issue is fixed in the last beta version (v1.20.3.b3) and in the last release (1.20.2.r4) of the firmware.