If you get the “can’t be opened because it’s from an unidentified developer,” my workaround has usually been right-clicking the app and pressing Open from that menu. That usually gets you to “are you sure?”
But there have been other, possibly loosely related issues between High Sierra and Insurgence, which you can see here, though I was on 10.13.2 when the issues cropped up. I had been fine on 13.1, and now I’ve updated to 13.3 and I’m back to normal.