IDK

Sometimes FA has kicked a few people off my watch list... So watching then leaving may be an FA issue...

Fur Affinity has +Watch / -Watch (and +Fav / -Fav) buttons that look very much alike.
I don't think it ever happened to me for watches, but I have been guilty of faving/unfaving/re-faving images because, in a moment of distraction, I clicked on the button of some image I liked, intending to add it to my favorites... without remembering nor noticing that it was already there.

An other possible scenario would be:
1) visitor peeks at the first page of your gallery and likes what they see, so they watch you;
2) visitor comes back soon after, with more time, to explore the remaining of your gallery;
3) visitor then discovers some contents they really dislike, which gets them to unwatch you.

And, finally, since we're on a furry site, there's the option that the visitor is an actual wild cat/raccoon, who interacts with the site mostly by walking on the keyboard and hissing at the screen. Thus some, uhm, erratic behaviors. That would explain /a lot/. ;P

I myself sometimes do it for the 1) 2) 3) scenario. I just wish FA would simply remove the notification from the dashboard but instead it lets you know "they watched you but then left". A bit needlessly cruel 😭

I also watch and de-watch if (for example) I think someone is interesting and I try to get in contact with them. But in a more…slow way. Seeing if they fave my stuff back, or if they leave a shout and then if they watch me back.

And if they don’t, I de-watch again. I know, this is not the usual reason why you should watch someone, but I do that x3

And of course it could be to the reason that people watch you until you watch them back and then de-watch to get more watchers while keeping they watched-list small. Like on Instagram: getting a huge following… to feel seen and all. If that makes sense.

Or they just missklicked.

Like another commentator said, sometimes you click the button on accident!

If it's immediate watch then de-watch, for me at least, like the previous two commenters, it's from accidental clicking (yeah I've done that before...).