Clean install of WP Engine. Clean install of Pro + child theme. Clicking on “Edit with Pro” always causes this issue. No other extensions or modifications have been made.
This was occurring with X as well before I contacted WP Engine support to refresh my install as well as ported over to Pro for $20. I’ve spent at least two hours inspecting similar threads trying to fix. No idea why this is occurring.
[CLOSED: Contacted WP Engine support and they were able to help me. If you use them and are having a problem, contact them!]