How to properly shut down M1 device in Micropython

accoding to the manual
https://www.digi.com/resources/documentation/digidocs/90002219/default.htm#reference/r_unavailable_at.htm?TocPath=XBee%2520module%257C_____1
the SD command cannot be used in Micropython. 5% of My modules no longer function after 6 months. ( they cannot read their own IMEI) I was told by Ankur at Digi to not use Airplane mode when putting the module to sleep but instead use “SD” how do I properly put the module to sleep if I cannot use ATSD command? I have been using
x.atcmd(‘AM’, 1) # Airplane mode before sleep
utime.sleep(30)
but this does not prevent corruption of the cellular module.
also afterwards I use:
x.sleep_now(90000,False)
this also does not prevent corruption of the cellular module. In 200 units, 12 have become corrupt within 6 months.