So for the first image, you see the activity on Aug 18th where the lead was deleted from SFDC... that's an indicator that the equivalent action was not taken (or no flag/boolean value set) on the Marketo side to stop future sync. That is why this one synced back via campaign "Run Action Add to SFDC..."
The second image looks to be your expected contact record from SFDC.
The third image is showing what seem to be the second lead.
Sometime between the 2:20 and 2:45 time frame on Aug 23rd that "Run Action Add to SFDC" campaign kicked off, and is the apparent reason why your leads synced to Salesforce.
Not sure how/why this happened based on these images, but somewhere to start looking.
Is this a triggered campaign or a batch update?
What initiated the run?
Again I would stress setting up the flags (boolean field) for "Sync to CRM", and only allow your campaign to sync if this is marked TRUE.
-Geoff
.png)