OK, thanks.
Possibly the server with the comment pics is also sometimes quite loaded, "attacked" by bots. Especially the forum of my own site which is on the same server. I previously tried to filter them, but like for IMCDb it was not easy to filter. So I'll maybe put Cloudflare on that one too, since it seems to work well for IMCDb itself.

When you upload a comment pic, the chain goes like this: your browser => Cloudflare => imcdb.org (main server) => pics.imcdb.org (that other server).
At some moments the other server is taking a little too much time to respond.
In the past, you just had to wait, but Cloudflare is not patient enough, displaying an error instead of waiting longer

For me, yes.
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I didn't encounter any issues when setting the main pictures recently.

But is it for uploading pictures to comments, or setting the main pictures? (as for comment pictures, it involves the secondary server, so I know where to search for issues)

I have the same issue as Andy, usually if I go back it uploads pictures at the second attempt.

When uploading pictures for comments? Not for other types of actions?

Also now, it happens often
https://ppt.cc/fgFjTx@.png

Just yesterday? Or does it happen often when uploading pics? (and I suppose you didn't have issues when enabling the bot filter previously? :D)

This happened to me from time to time while I was uploading pictures
https://ppt.cc/fzFTDx@.png

You can leave it as is, Antoine. Really it is fine as long as those annoying invisible ad pop up at the bottom and sides doesn't come up.

What do you mean exactly by that?
In case you are using the site without being logged in, there is a 0.5 delay added when loading a page. This was added when we had issues with bots not detected as bots, maybe I should remove it.
But it does not affect users who are logged in.