Curious, have you gotten an update on this? An issue I saw recently occur happened when a single webinar I had scheduled was launched likely in error three times by the organizer which created three separate attendee reports. As a result of these multiple reports, only the first report with attendees (2) was pushed to Marketo, when there really was 70. I would be interested if all attendee reports can be synced? I have been talking with Citrix development and they think it is a Marketo issue.
Last update from Citrix was the issues would be fixed by end of Q1 2016.
Regarding your issue: starting and stopping the webinar create sync issues. I have also experienced it. I believe Citrix tells Marketo via the API the webinar is over so the lead status can be updated. so when you start it again, nothing syncs back.
I feel for you as I had to battle my way via Marketo support get them to talk to Citrix engineering to establish were the issue is really coming from.
Suggest you open a ticket with both but first confirm from Marketo support that starting and stopping and restarting the same webinar impacts sync of leads.
Keep me posted. I am curious to know more