User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:109.0) Gecko/20100101 Firefox/111.0

Steps to reproduce:

"From" and "Subject" are sometimes still missing in 112.0b3 (MacOS), three-pane view.
Same goes with attachments. The bar at the bottom of the message pane is missing, too.
Switching a few times between different messages may or may not bring it back.
There is no clear inidicator why this happens with certain messages.

Richard, is this a theme issue? See screenshot in attachment 9324643 [details].

Quadroon, from message header of affected msg, can you please do More > View Source and check if From and Subject header are present in the source of the message?

No, this isn't a theme issue as the reporter wrote it's not on all messages.

Quadronom, does this happen only in one folder? Then maybe a repair folder could help.

@ Thomas: Yes, in the source everything is present, neat and tidy.

@ Richard: No, it happens in all folders. I wanted to say it happens rarely, but one in 15ish is not really rare. Switching between different messages will bring it back sometimes.

This is really urgent and severe. It became worse.
After some attempts it was always working for a moment, now in 112.0b7 it always fails consistently. Which means there is no way of obtaining the attachments...

This is not a dark mode issue as the visibility of the data is not related to themeing.
We updated the code that clears the message pane and loads it properly when switching messages, does this still happen in daily?

Sorry I had no time to look at the daily builds to see if there was a remedy, but I can tell that in 114.0b6 I couldn't reproduce it yet. In 114.0b5 it happened very frequently and with the same emails, those seem to be ok now. I will keep an eye on it tho.

Update: It still occurs with 114.0b6.

I was finally able to reproduce this and I can confirm is a duplicate of bug 1819916. Same issue there.
Opening the folders properties dialog and clicking on "Repair folder" fixes the issue, but then it reappears randomly.
We're investigating.