Stacks relies on the old WebView framework, which Apple deprecated in 2014
and replaced with the more modern WKWebView. As a result, graphics in Edit mode—especially when hardware acceleration (GPU) is enabled—can glitch out, causing stacks to vanish or display incorrectly.
I don’t have time to dig up every old post that covers this issue, but here’s a thread from 2024 where the “Shelf” stack in Foundation 6 was causing problems. The fix in that case was to disable the “Turbo scrolling” option:
Since WebView is deprecated, the only real long-term solution would be for Stacks to migrate to WKWebView—but from what I’ve gathered, that isn’t likely to happen. There was a discussion about WebKit on the Stacks Discord just yeterday, but you need a login to view it so I’ve included the relevant part below.
If these kinds of rendering glitches are starting to become a pain, it might be worth exploring alternatives. You probably know where I’m going with this 
The Elements editor uses the modern WKWebView (and it’s SUPER FAST) under the hood, so editing is snappy and visually accurate. Might be something to look into if you’re running into these issues regularly!