You have a custom sync filter in place between your CRM and Marketo. You mark a number of records in your CRM as blocked from the sync and go to Marketo, intending to delete them. However, the records in Marketo have not been updated with the blocked from sync value in the sync filter field.
The Marketo Sync Filter looks at the CRM to verify if a record's updates should sync to Marketo. This means that if the sync filter field is updated to a blocked value on the CRM side, that value will not be pulled into Marketo. If you'd like that field to be updated in Marketo, you can do one following options:
Export a list of the new blocked leads with their sync filter field values and use the list import to update those values on the Marketo side.
Create a Smart Campaign to update the sync filter field value on the Marketo side.
Make the initial update on the Marketo side, since the block will not go into place until the value is pushed up to the CRM by the sync.