I’m pretty much using ACF out of the box too, just using get_field and the_field to retrieve the values. I think it is only happening on archives.
Another person made the same complaint at: https://wordpress.org/support/topic/image-field-not-returning-url-in-archive-loop-following-update-to-5-7-8/
I ended up just restoring my site to a backup from a few days ago before I updated the plugin – could not afford downtime for my client.
