Hello. I just almost had a heart attack because it seemed like half of my page was suddenly gone. But since I've been working on Appsmith quite a bit, I kept my cool and figured out what happened. However I'm not sure someone new to Appsmith would be so fortunate. Maybe this is a well known problem already but if not it's something to look into I think.
The gist of the problem is that when you copy/paste widgets and particularly when you then undo actions you may end up with hidden widgets. I can't show you exactly what happened to me, but I have a couple of screenshots that show the gist of the problem.
In the first screenshot there are two containers that enclose the header and the main area. Note the selected text widget Text10.
In the second screenshot I have copy/pasted Text10 with the result that the button at the bottom of the container, "Skapa följesedel" seemingly disappears.
Now this is a "mild" version of what I experienced. In my case after messing around with a couple of widgets that pushed things around when I copy/pasted them, I decided to revert and did a number of undo actions. And ended up with a layout that looked like Text10 was the topmost widget in the container! The two top rows with select widgets had been "shoved upwards" and were completely hidden from view. Expanding the container revealed them again, but before that there was no visible hint of them still being there.
If an "inner" layout grows any wrapping widget needs to grow also to make sure that nothing become hidden. Automatic stuff should not surprise you!