In Spring'16 release Salesforce introduced Files uploaded to the Attachments related list on records are uploaded as Salesforce Files, not as attachments
in Salesforce Files Settings:
Files that you upload to the Notes & Attachments related list on records in Salesforce Classic are now Salesforce Files objects, rather than the old attachment objects. A new org pref in Salesforce Files Settings controls this behavior, and is enabled by default for new orgs.
The following SOQL query would allow you to get Ids of Files (Attachments) and New Notes related to the record SELECT ContentDocumentId,Id,LinkedEntityId,ShareType FROM ContentDocumentLink WHERE LinkedEntityId = 'YourRecordId'
SELECT ContentDocumentId,Id,LinkedEntityId,ShareType FROM ContentDocumentLink WHERE LinkedEntityId = 'YourRecordId'
it's possible you haveFiles uploaded to the Attachments related list on records are uploaded as Salesforce Files, not as attachments
enabled for your org.