Salesforce Pull for Record ID’s

I am currently working on mapping objects. I have read documentation and have been experimenting with the plugin to learn the in’s and out’s which has been great so far. Before I got too much further I wanted to reach out and ensure that I understand this some things correctly. I have had success pushing new records into Salesforce. I can update existing records for mapped WP records in Salesforce with no issues.

1. When I create records in Salesforce to push into WP I run into problems. Here is one of the logs “The WordPress tribe_events with of 876 is already mapped to the Salesforce Event__c with Id of a0kQL0000004dUDYAY in the mapping object with id of 71. The Salesforce Event__c with Id of a0kQL0000004dUDYAY was created or modified in Salesforce, and would otherwise have been mapped to this WordPress record. No WordPress data has been changed to prevent changing data unintentionally.” I attempted to create a new record in SF and push it to WP. 876 did exist but the SF record did not have a Post ID which I am using as a Pre Map so I was expecting a new record to be created in WP. I am not sure what I am missing.
2. Also, is it necessary to create custom fields in WP to hold the Salesforce Record ID or is that unnecessary? Seems to work without it but I created a custom field using ACF to hold the SF record ID and then mapped it. I have been unable to push record ID’s from Salesforce into the custom ACF fields. I read about needing to have a value before they are available to map and did successfully map it but I can’t push Salesforce ID’s over. Just want to make sure I understand how that is supposed to work. Thanks!