Hi there,
It’s frustrating that everytime Elementor cannot find a solution they blame it on the theme.
GeneratePress is actually the theme they suggested to use when debugging.
Unfortunately that is not an issue with GP. No code on that page should be coming from GP.
I would recommend starting by keeping GP and Elementor activated only and see if the issue is resolved.
If not then contact their support again for a better answer.
If they still think it’s an issue with GP, please ask them to elaborate.
We have tons of customers using GP with Elementor without this issue.
Let me know if this helps 🙂