I have exactly the same problem, I built a kind of page builder with ACF Flexible Content Fields and I have ridiculously long loading times on the admin edit page where Yoast SEO plugin is activated.
Does anyone found a solution for this issue ? I’ve been digging a bit and it seems that the problem comes from the “Schema” tab in the Yoast SEO module. But didn’t find a way to deactivate it without breaking the whole thing…
