In Japan, we often use the letter '×' (Unicode 0x00d7) to indicate quantities of commodities on quotes, shipping lists, etc. as like 'iPhone SE × 10'.
On Jira Service Management (Cloud), we have a screen which have a text field. When we create a new issue, Jira sends us an e-mail and in the body '×' is substituted with '×'. On the subject of the same e-mail, this substitution does not happen.
Somewhere in Jira, in the pipeline from the screen to the e-mail, HTML sanitization and/or codec process should be causing this.
Since unfortunately Jira is now going away from open source, we can not dig into the source of the problem. Please check this issue.