Similar symptoms as described in https://community.atlassian.com/t5/Jira-questions/How-to-fix-quot-failed-to-load-quot-error-at-attachments-in-Jira/qaq-p/952044 but not matching any of the characterizations there.
Some, not all attachments fail to load are not accessible. The attachments are accessible in the Old Issue View.
Screenshot:
There are linked issues, but it is not clear that that has anything to do with the error.