Remember that pet journal bug that was causing names to display all lowercase after using searching tool?
Now, it seems it has extended to a worse condition.
The names tend to disappear, either partially, or completely.

A sample: https://i.imgur.com/vwZcwPR.png

Yellow dots show partially removed names. Red dots show these entirely cleared out. As you can see, I decided to disable addons to no avail.

What helps:

Avoiding to use search tool.

/reload.

What else remember to do:

Backup your holy trinity (Cache, WTF, Interface). The WTF alone should do, but better safe than sorry. (Although the names are stored server-side, aren't they? – you need to prevent addons from interaction with duplicates etc.)

/reload UI each time you're gonna logout/leave the game, to avoid possible name loss

OR exit game by killing the process (caution: this prevents the game from saving ALL session changes, not just bad ones)

Mini-Cataclysm indeed.