Any hints on where to look to fix these performance issues would be appreciated.
However, our main issue is this:
If the client updates something at the top of the page (ie. an image or the title) and then hits Update before ACF has finished loading all repeater blocks, anything not loaded yet will be cleared from the page.
So, saving before ACF has loaded will delete content from posts.
Is it possible to disable the save button while ACF is loading?
I looked into this a bit more and I think I found the culprit. The flexible content blocks have a Link dropdown, and the sheer number of pages on this website makes this list huge. On the page I mentioned above, 4.1Mb is transferred, most of this is content relating to the link field.
I understand this has been fixed in ACF5(?) so I’ll try upgrading and see what happens.