Occasionally, all the enrolments seem to disappear from a course for no apparent reason. Except there is a reason - it's because the Moodle cron has not completed correctly.
Checks to make
Check is to see if the cohorts are populated under Site administration > Users > Cohorts. Find a ZiLink Cohort which is enrolled in the course and see if the cohort size is zero. If it is zero, initiate a Cohort Sync on ZiNET Connect.
If it is not zero, then the cohort contains students.
Then go to Site administration > ZiLink > Cohorts > View and select a relevant cohort. You should see members of the cohort.
At this point we know the cohorts are actually populated.
The final step is to go to the Course administration > Users > Enrolment methods and check the list of cohorts. If the cohort size in this list is zero, add another cohort using the 'ZiLink - Cohort Sync' method. This will have the effect of triggering cohort enrolments (something the cron job would normally do) and when you return to the list you should see the cohorts have populated which, in turn, will mean that the students are enrolled again.