FlightCreative’s link above fixed the issue for me.
For reference, what this does is turn off the tabbing that ACF introduced to tidy up the individual fields (where you conditional logic and other things would be on separate tabs) and reverts it back to the old view where it’s all in one long list.
The difference is DRAMATIC. I’ve gone from an unusable 45seconds loads time to a second or two.
And this is a pure layout thing – no functionality is lost.
