Just to confirm
a) there is actually a bug in the completion cron and we have a patch in review
b) The nature of the bug means that in order to correct the totals on the My Team report for courses already completed we also need a data manipulation upgrade script, which will be an upgrade to the totara_core module, though the bug itself is a one-line change
c) The course completion totals on the My Team report should, when the bug is fixed, be updated on every run of the cron, not overnight as I previously mentioned.
If you want to correct the bug yourself then in file lib/completion/completion_completion.php, line 310, change
$data['eventtype'] = STATS_EVENT_COURSE_STARTED;
to
$data['eventtype'] = STATS_EVENT_COURSE_COMPLETE;
Which will/should start picking up any courses completed after this change is applied. But the correction of the totals for any courses already completed should probably wait for the official patch.