I have a reproducible bug where attaching a .txt file and a .png file in the same (multi-file) upload action causes the "Error rendering 'com.atlassian.jira.jira-view-issue-plugin:attachmentmodule'." error to appear.

Attaching each separately is fine. Going in, removing all attachments, then re-attaching each separately resolves the issue as well.

This was under v6.3.15#6346-sha1:dbc023d

I do not know if the underlying error is still present in version 6.4, because of the new upload interface that technically uploads each file individually even when bulk uploading, the problem does not appear in v6.4.3#64018-sha1:4550402 - it is not possible to confirm it has actually been fixed on my end.

I have attached the full log for the test case described.