Thanks for the login details.
I am quite sure that the performance issues are coming from your server, not from ACF.
When I edited the fiedl group (which only contains 5 fields), the page took quite some time to load and appears to load in broken sections.
The reason why the ‘sample page’ is so laggy, is because the page also loads slowly in broken sections, and then only once it has fully loaded, can the JS run.
The lag is not from JS, but from PHP.
I would consider upgrading your server, or developing on a local host for now.
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