Hello there.
My issue sounds similar to https://community.atlassian.com/t5/Jira-Service-Management/Customer-replies-to-ticket-emails-not-appearing-in-ticket/qaq-p/2177487.
It occurs intermittently, not for all of our internal Requestors. Most recently, one of them replied to an existing ticket through the copy they received with jira@myCompanyOrg.atlassian.net but it did not show up in the Case.
From: <my customer's email address... who also is the ticket Reporter>
Sent: Wednesday, January 25, 2023 12:51 PM
To: jira@myCompanyOrg.atlassian.net
Subject: Re: [EXTERNAL]: Following up on your ticket [the ticket number]
She was replying to an email that the system sent to her. Any suggestions?