Interesting -- my first thought was that it was a screen-resolution issue, but I'm seeing the same exact thing. I applied the same Audio Unit effect (that's a built-in Apple AU multiband compressor).
The workaround is to enable the Inspector (top right-hand corner of your screen in Resolve) and scroll down; you'll see all the individual controls for the compressor there. But the popup window is not scrollable and doesn't show the details when the "Details" twistie is expanded.