Hi @elliot,
this is still an issue for us in the most current version (5.8.9).
I was able to narrow it down to acf_get_valid_post_id() which seems to return a wrong post_id in these preview cases – don’t know whether the returned post_id is of a revision? I don’t quite get everything that’s going on, tbh.
Could you please have a look? Would be great to get this working again. Our clients are asking for it, they would like to preview drafts…
Cheers mate 😉
Moritz
