I am also experiencing higher-than spec’ed sleep current (610uA measured), but using the Boron LTE Feather module with deviceOS 3.0.0, as noted in my post here.
There are some others in the Forum experiencing similar with Argon hardware and deviceOS 3.0.0.
There seemed to be lots of Forum activity around sleep current issues around deviceOS 1.5.0; Based on the comments at the end of that thread, I may target some older versions and see if there was a regression in terms of sleep current. If I do, I will post my findings.