My watch, Garmin Forerunner 35 has not been registering my steps today, it last registered the steps for Monday 08 March and nothing on Tuesday 11 March.
The FR35 is notorically known for having problems with full storage, so make sure to clean up the folder //GARMIN/Activitiy/ regularly (over the USB cable), to make some free space, in order that there is enough room for new data.