I think the current dev branch (1.5.7dev) has a glitch for the BG chart units.
I deleted all Loops apps from phone, deleted Health BG data, set the units to mmol, and built a fresh Loop from a download of current dev branch. Used a mmol share account as the source of BGs for Loop.
the settings are all coming up in mmol units...but the BG chart is displaying in mg/dl. BG data in Health app is in mmol.