@daniel I did try to erase the flash using esptool and then flashed 1.9.2.b2 with updater.py. Unfortunatelly L01 soldered on OEM baseboard is unstable in case WiFi client connects to it. ets Jun 8 2016 00:22:57 rst:0x1 (POWERON_RESET),boot:0x12 (SPI_FAST_FLASH_BOOT) configsip: 0, SPIWP:0xee clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00 mode:DIO, clock div:1 load:0x3fff9010,len:12 ho 0 tail 12 room 4 load:0x3fff9020,len:388 load:0x40078000,len:11584 load:0x4009fb00,len:848 entry 0x4009fc9c MicroPython v1.8.6-796-g489fafa0 on 2017-10-15; LoPy with ESP32 Type "help()" for more information. >>> os.uname() (sysname='LoPy', nodename='LoPy', release='1.9.2.b2', version='v1.8.6-796-g489fafa0 on 2017-10-15', machine='LoPy with ESP32', lorawan='1.0.0') >>> import time >>> while True: ... print(time.time()) ... time.sleep(1) ... ... ... 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 Guru Meditation Error of type IllegalInstruction occurred on core 0. Exception was unhandled. Register dump: PC : 0x40151ff4 PS : 0x00060630 A0 : 0x80152198 A1 : 0x3ffb6e10 A2 : 0x3ffb6e60 A3 : 0x00000002 A4 : 0x0000000a A5 : 0x0000000a A6 : 0x00000000 A7 : 0x0000000a A8 : 0x00000000 A9 : 0x00000008 A10 : 0x3ffb6340 A11 : 0x00000000 A12 : 0x00000000 A13 : 0x3ffb6eb4 A14 : 0x0000000a A15 : 0x00000000 SAR : 0x00000019 EXCCAUSE: 0x00000000 EXCVADDR: 0x00000000 LBEG : 0x4000c2e0 LEND : 0x4000c2f6 LCOUNT : 0xffffffff Backtrace: 0x40151ff4:0x3ffb6e10 0x40152195:0x3ffb6e40 0x401523e7:0x3ffb6e60 0x40152b2c:0x3ffb6e90 0x40143335:0x3ffb6eb0 Guru Meditation Error of type LoadProhibited occurred on core 0. Exception was unhandled. Register dump: PC : 0x40089d09 PS : 0x00060033 A0 : 0x80088b46 A1 : 0x3ffb6a50 A2 : 0x3ffb6aa0 A3 : 0x3ffb6a70 A4 : 0x00000000 A5 : 0x3ffc482c A6 : 0x00000000 A7 : 0x3ffc4848 A8 : 0x00000012 A9 : 0x3ffb6a20 A10 : 0x3ffb6ae8 A11 : 0x3ffb6a70 A12 : 0x3ffc4bb8 A13 : 0x3ffb6e40 A14 : 0x3ffdbca8 A15 : 0x3ffb6e60 SAR : 0x00000014 EXCCAUSE: 0x0000001c EXCVADDR: 0x00000000 LBEG : 0x4000c2e0 LEND : 0x4000c2f6 LCOUNT : 0x00000000 Backtrace: 0x40089d09:0x3ffb6a50 0x40088b43:0x3ffb6a70 0x4008ae65:0x3ffb6aa0 0x4008b1da:0x3ffb6c70 0x4008aae5:0x3ffb6cb0 0x4008ac60:0x3ffb6d30 0x40081672:0x3ffb6d50 0x40151ff1:0x3ffb6e10 0x40151ff1:0x3ffb6e40 0x401523e7:0x3ffb6e60 0x40152b2c:0x3ffb6e90 0x40143335:0x3ffb6eb0 Guru Meditation Error of type LoadProhibited occurred on core 0. Exception was unhandled. Register dump: PC : 0x40089d09 PS : 0x00060033 A0 : 0x80088b46 A1 : 0x3ffb6690 A2 : 0x3ffb66e0 A3 : 0x3ffb66b0 A4 : 0x00000000 A5 : 0x3ffc482c A6 : 0x00000000 A7 : 0x3ffc4848 A8 : 0x00000012 A9 : 0x3ffb6660 A10 : 0x3ffb6728 A11 : 0x3ffb66b0 A12 : 0x3ffc4bb8 A13 : 0x3ffb6a70 A14 : 0x3ffb6aa0 A15 : 0x00000020 SAR : 0x00000019 EXCCAUSE: 0x0000001c EXCVADDR: 0x00000000 LBEG : 0x4000c2e0 LEND : 0x4000c2f6 LCOUNT : 0x00000000 Backtrace: 0x40089d09:0x3ffb6690 0x40088b43:0x3ffb66b0 0x4008ae65:0x3ffb66e0 0x4008b1da:0x3ffb68b0 0x4008aae5:0x3ffb68f0 0x4008ac60:0x3ffb6970 0x40081672:0x3ffb6990 0x40089d06:0x3ffb6a50 0x40089d06:0x3ffb6a70 0x4008ae65:0x3ffb6aa0 0x4008b1da:0x3ffb6c70 0x4008aae5:0x3ffb6cb0 0x4008ac60:0x3ffb6d30 0x40081672:0x3ffb6d50 0x40151ff1:0x3ffb6e10 0x40151ff1:0x3ffb6e40 0x401523e7:0x3ffb6e60 0x40152b2c:0x3ffb6e90 0x40143335:0x3ffb6eb0

@jmarcelino Yes, my problem is the same as what you highlight, thanks for solving the mystery. As an temp solution (for lazy ppl) I can suggest : # hard reset if last was a soft reset if reset_cause() == 4: reset() if not 'sigfox' in locals(): sigfox = Sigfox(mode=Sigfox.SIGFOX, rcz=Sigfox.RCZ4) Regarding the UART1 activity causing Sigfox instability, I will do more tests later. Maybe update the SiPy pinout PDF to include the UART1 pins (like LoPy) as @livius mentioned?