export a subsite webpart could not be found, or is not registered as saf

A few options you can use to get the web part using GUID:

1 Iterate through every web part page in the subsite. Try using SharePoint Designer 2013 to open the pages and search for "WebPartId" and see if you can get the result.

2 Run database query on all content databases, which might be different based on which version of SharePoint you are using.
Here is a sample query for SharePoint Server 2013:

SELECT DISTINCT D.SiteID, D.WebId, W.FullURL as WebURL, D.Id As DocumentId,  
                D.DirName, D.LeafName, tp_ID As WebPartSK  
FROM       dbo.Docs D WITH (nolock)   
INNER JOIN dbo.Webs W WITH (nolock) ON D.WebID = W.Id  
INNER JOIN dbo.AllWebParts WP WITH (nolock) ON D.Id = WP.tp_PageUrlID  
WHERE WP.tp_ListId Is Null AND WP.tp_Type Is Null AND WP.tp_Flags Is Null  
      AND WP.tp_BaseViewID Is Null AND WP.tp_DisplayName Is Null   
      AND WP.tp_Version Is Null  
AND WP.tp_WebPartTypeId='<your web parts id>'  

Please refer to a post with similar request here for further information: Sharepoint find where webpart is in use.

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The SharePoint Version is 2016 and the above step did not help.

I refered the below forum link and able to get the faulyt webpart ID by querying the database

https://social.technet.microsoft.com/Forums/en-US/4be045fa-5201-4a2b-89a5-8cd767c2ec5d/how-to-find-out-if-and-where-a-webpart-is-used?forum=sharepointadminprevious

Located the bad markup rows.

Removed it by using SQL Query. I know that it is not advised to execute the SQL query in the Content Database. Please advise.

After this export log does not show any error or warning.