INVALID_CROSS_REFERENCE_KEY : Invalid cross reference id in After insert Trigger to create ContentDocumentLink

I am encountering the following error when inserting a ContentDocumentLink record :

Error [statusCode=INVALID_CROSS_REFERENCE_KEY, code=[xmlrpc=1202, statusCode=INVALID_CROSS_REFERENCE_KEY, exceptionCode=INVALID_CROSS_REFERENCE_KEY, scope=PublicApi, http=400]

The insert operation is in an After Insert trigger on the object ContentDocument, I am trying to link the newly created ContentDocument with an existing Account. I already checked the following options :

• Checked that the Account Id in the LinkedEntityId fiel, and the ContentDocument Id in the ContentDocumentId field of ContentDocumentLink record are valid Salesforce Ids;
• The file is correctly uploaded and visible in Salesforce;
• I also tried with Ids in static strings of the existing Account and an already existing ContentDocument, and it didn't throw this error. I know that it is possible to create a ContentDocumentLink when a ContentDocument is inserted, since I already implemented it in another project but I no longer have access to the code.

Any tips on what I am missing would be greatly appreciated.
Thank you.

EDIT #1 : Trigger Handler code

List<ContentDocumentLink> doclinksToCreate = new List<ContentDocumentLink>();
   Map<String, String> docIdsToAccountIds = new Map<String, String>();
    Map<String, String> userIdsToDocIds = new Map<String, String>();
    for(ContentDocument oneDoc : docs){
        userIdsToDocIds.put(oneDoc.CreatedById, oneDoc.Id);
    }

    // Get a list of AccountIds related to portal users that created ContentDocuments
    List<User> portalUsers = [SELECT Id, AccountId, Account.Name, Profile.Name 
                            FROM User 
                            WHERE Id IN :userIdsToDocIds.keySet()
                            AND Profile.Name = :System.Label.TheProfileName];

    Set<String> accountIds = new Set<String>();
    for(User oneUser : portalUsers){
        docIdsToAccountIds.put(userIdsToDocIds.get(oneUser.Id), oneUser.AccountId);
    }

    for(String key : docIdsToAccountIds.keySet()){
        doclinksToCreate.add(new ContentDocumentLink(
            ContentDocumentId = key, //'0693M000000fhOcQAI'
            LinkedEntityId = docIdsToAccountIds.get(key), // '0013M000018llyNQAQ'
            ShareType = 'I',
            Visibility = 'AllUsers' 
        ));
    }

    Database.SaveResult[] results = Database.insert(doclinksToCreate, false);
    Database.SaveResult oneRes;
    List<String> accountsIdsToNotifyAbout = new List<String>();
    for(Integer i=0, size = results.size(); i<size; i++){
        oneRes = results[i];
        if(oneRes.isSuccess()){
            System.debug('Insert document link success for document with Id : '+doclinksToCreate[i].ContentDocumentId);
            accountsIdsToNotifyAbout.add(doclinksToCreate[i].LinkedEntityId);
        }else{
            System.debug('Error with document Id : '+doclinksToCreate[i].ContentDocumentId);
            for(Database.Error oneError : oneres.getErrors()){
                System.debug(oneError);
            }
        }
    }