Are you filtering the sync? In which case it may come that the leads in SFDC were not marked as "sync with Marketo".
The other possibility could come from the way your roles are set up in SFDC, making these leads hidden from Marketo for a while until their user was changed.
Thanks for the response. Yes we do use the "Sync to Marketo" filter in our sync. I should have mentioned in my post that I already investigated that avenue. None of the Leads in question appeared to be blocked from the sync at any time. (We have a SFDC workflow that automatically sets this sync field to YES for any lead created by our Marketo Sync User). I looked at a Data Value Changed smart list on this field during the timeframe and did not find any results.
I do understand what you're saying about the second possibility -- yet I don't think it would be the issue either. The records are shown in SFDC as Created by our Marketo User, so I don't think they could have been blocked from its visibility as they were created by it. Also we have several hundred new leads per day that get created by Marketo then inserted to SFDC, and we haven't see this issue other than during the 3 or 4 day timeframe that I'm looking at.
On the first point, If you set the "sync with Marketo" field to "False", Marketo will not know and will not show a "change data value" as the sync will stop immediately, before pushing the updated value to Marketo. Read here "Sync with Marketo" mysteries part 1 for more details, so this might be the issue, still. You need to track field change on SFDC side to be sure.
More globally, in this case I would make sure that 3 fields are tracked on SFDC side, in the SFDC field history:
- lead status
- lead owner
- sync with Marketo
If the issue occurs again, I would then audit them on SFDC side as well.