Unfortunately, this has been an issue way longer back.
I have made them a ticket, describing in details in which use cases the Preview-feature that does not work, and when it works.
So knowing the problem – makes the solving much easier.
But they have not even replied me yet for a couple of weeks – and I did put 40 hours to test various conditions and different things to really get to bottom with this.
It all comes down to how revisions are internally organized within the WordPress core – but the solution is not that hard – but they still have the job to do.
I have been using ACF since the very beginning 😉
