I deactivated PowerPack Pro and switched from Neve Pro theme to Elementor’s “Hello” theme. This was the only thing that worked. Neve and PowerPack Pro support both insist that they are compatible, but I had the error show up with each one separately after deactivating all other plugins. I still think that the problem is that Elementor is becoming too buggy and just no longer works well with even a small number of well built and widely used plugins. They need to fix this problem urgently.