Sometimes the picker just refuses to be summoned.
Bluetooth is a mess. File transfers will fail, who knows why? Certainly not macOS. Often I'll just punt to GoogleDrive-TP.
Really random screen wakes.
Left macOS alone for 5s? All your windows have decided to start playing a game of musical desktop, and need 10s to re-arrange themselves back into place, also while sometimes displaying their contents at 2x.
Slack has any number of these; e.g., emoji inside codeblocks are simply corrupted. A number of odd corner cases in URLs will corrupt, and each edit of the message will further corrupt it.
So much of the web is plagued by some framework that, upon any JS exception, will destroy the entire DOM (idk maybe defunct page > no page at all?) and leave you only with "ApplicationError: …".
At this point I'd add "is a motorcycle a car? Is a pedestrian signal a stop light?!" CAPTCHAKCAS to this list, but those are a "feature".