Sometimes when I try to save an image, it saves as ".webp" instead of a png or jpg. It seems to only happen with thumbnails, whenever an image is uploaded where you can click on it to expand it always saves normally. I'm on mobile using Brave Browser for Android, in case that's in any way relevant.
Also, on mobile, there seems to be no indicator whether a thread in the Watched Threads list has unread messages or not, but if I use the desktop layout of the site there's a little dot that's filled in next to it if there are unread messages.