Creating multiple attachments asynchronously returns HTTP error 500

[Kerwood]

I have created an application for updating my Confluence page with content using the API.

I can upload multiple attachments synchronously using this endpoint Create or update attachment, but if upload 2 or 3 at the same time asynchronously I get a HTTP 500 error back.

 I can't find any restrictions on that API endpoint, nevertheless, an API restriction should not return an error 500 back