Hi Marouene,
Change that Timer to 1 (for one hour), and see if resets after one hour instead of 20 mins.
Alternatively, you can do a factory reset on the device, and then upgrade to the new firmware and see if that resolves the issue.
Or, please contact your reseller for further assistance as they will need to check the logs to find out what’s causing the reset every 20mins. If you do not know who your reseller is, or they could not provide you the proper support you’re looking for, please create a ticket:
sierrawireless.com/support/makerequest/
Thanks,
J.