Beware bizarre bug in Mail app on Apple devices

Evidently the Mail app occasionally swaps the message body of emails. I have found people reporting this bug as far back as 2012, and it happens on iPhones, iPads, and Apple laptops and desktops. Looks like for some folks they click a mail header and it opens a completely different message. When it just happened to my wife, she forwarded a message and Mail included an old unrelated email that she had previously received from a different contact. Thankfully no sensitive information was disclosed this time, but as you can imagine this bug can cause a lot of confusion.

All of the responses that I've read from Apple support indicate that they are bamboozled by this one, and it seems they haven't figured it out in over a decade. "Fixes" include turning off message threading (it was already turned off in this case) and "rebuilding" the account (which is hit or miss according to other users). Apple tends to suggest wiping the phone and reloading everything, which is a huge pain and obviously is not a fix for what causes it in the first place.