Steps to reproduce

1. Create a project name 'Test'
2. Create a custom field type Select List name 'Atlassian'
3. Add a few options in it such as 'JIRA', 'Confluence'
4. Create a new issue type 'Bug' with and select 'JIRA' for custom field 'Atlassian'
5. Create an XML backup
6. Delete the project 'Test'
7. Edit the Configuration of the custom field 'Atlassian' so that it is limited to the Issue Type 'Bug' only
8. Restore the project 'Test' by using Project Import
9. There will be an error during the validation:

The custom field 'Atlassian' requires option 'JIRA' for the import but it does not exist in the current JIRA instance.

 
Workaround
Edit the configuration of the custom field 'Atlassian' so that there is no restriction for Issue Type (All Issue Type selected)

Administration -> Fields -> Configure (the gear on the right of a custom field) -> Edit Configuration for Applicable contexts for scheme -> Issue Types -> "All issue type" option.

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Some users have also experienced similar errors when importing custom fields due to trailing white space in custom field names. If you're getting a similar error, double check that your Custom Field names align exactly between the two instances.