Just updated to 5.7.0 and noticed this issue. When getting the image field url from an image field within a repeater like so: get_sub_field(‘image’)[‘sizes’][‘some-size-name’] and the image doesn’t have a crop saved at ‘some-size-name’ acf used to get the next available size image url, but now it fails. Re-installing 5.6.10 makes it work again. I’ve only noticed this in images fields that are part of a repeater, stand-alone image fields seem fine so far.
You should probably submit this as a bug by opening new support ticket for his here https://support.advancedcustomfields.com/new-ticket/ or maybe here https://www.advancedcustomfields.com/contact/, not quite sure which is the right one to use any more with recent changes to the site.
