Email text not displaying in history

Transaction is posted in history, and images (like from signature) show, but the text of the message is not displayed. Clicking “View Source” or “View Source with headers” opens a new tab where the message text exists. For example:

Content-Transfer-Encoding: quoted-printable
X-RT-Original-Encoding: utf-8
content-type: text/plain; charset="utf-8"
Content-Length: 851

Anna -
This is in my court. I have a call with Scott...

Other messages in the ticket show their text without any problem.

Oops. Forgot to include specs:
RT Version 5.0.2 (on-premise)
AlmaLinux 8.7 on VMware
mysql Ver 15.1 Distrib 10.3.32-MariaDB, for Linux (x86_64) using readline 5.1
(db on separate AlmaLinux VM)

Problem exists on every browser tested – Chrome, Edge, Firefox

Is this happening with all messages, or just some? Are the users affected all using the same mail client when this happens? I’m wondering if a mail client is sending some weirdly MIME encoded multipart or something.

The other option I can think of (and its a long shot) is try changing to dark mode and seeing if there’s any CSS that is making the text white on a white background.