LoPy Invalid syntax error after DeepSleep

Please include the following information when submitting a bug report:

The Pycom board you are using (e.g. WiPy 2.0, LoPy). LoPy L01 OEM
The firmware version you are using. You can get it by executing the following Python code at the REPL: (sysname='LoPy', nodename='LoPy', release='1.18.2.r3', version='v1.8.6-849-a1641ca on 2019-02-28', machine='LoPy with ESP32', lorawan='1.0.2', pybytes='0.9.10')
Exact steps to cause this issue A group of LoPy boards were set up with the machine.deepsleep() function to send a message using LoRa every 15 minutes.
What you expected The devices should wake every 15 minutes, send a message and go back to deepsleep. This cycle should continue until the device is turned off.
What happened instead All of the devices crashed with a "Invalid syntax error" after random amounts of time. Some after around 6 hours, while some worked for 5 days. The error pointed to different (seemingly random) lines on each of the boards, which were succesfully executed during previous cycles.
Additional information
1. This issue was also observed on LoPy boards using the 1.18.2.r6 release.

Any information on possible fix or workaround would really help, as I don't want to fully rely on WDT. Kind Regards, H.

pycom / pycom-micropython-sigfox