Search service error

I have created a new search service on a site collection - SharePoint 2016 on prem. I ran full crawl then when I checked the crawl log I found about thousands error with the message: The SharePoint item being crawled returned an error when attempting to download the item. ( SearchID = XXXXXXXXXXXXXXXXXXXXX) and a URL which takes you to the documents.

I can surf to the URL, I find the documents, I can open then and I can search and find these documents but I don't understand what's the problem that generate this error messages.

Regards

Ashraf