I have the same problem but here is what I know. I see by your screen shot you are using "Dark Mode" which can only mean you have macOS Mojave installed. The problem is not ad block but the new macOS/safari that is causing the issue. Apple no longer allows stand alone safari extensions. Developers need to develop an application (which you will see in your Applications folder) that run when safari is started. If you look in your extensions tab in the safari settings Apple even warns you about this extension! This is typical Apple changing the game. It is yet to be seen if this will actually make improvements is safari's speed or not. I am also very frustrated as I very much enjoy surfing with Adblock. I hope this information helps you understand what's happening but until Adblock publishes a new version for macOS Mojave I think we have to live with this or find another solution.
It should be noted, I have been running all the latest version of Adblock on macOS 10.13 with no issue. It has only been the Mojave version I have been running on a test machine that displays this same issue.
My solution for now was to switch between Firefox and Chrome and only use Safari for Apple sites like iCloud. Both Firefox 62 and ESR releases have been running fine on 10.14 as well as Chrome 69.