I have a home-grown plugin that (long story short) takes a post's featured image and attaches it to an email and sends on publish.
This worked just fine up until the latest WP release. Now it seems the attachment only works when the publish is now/immediate. However, when a scheduled post publishes the email is sent but the feature image isn't attached. I know that sounds strange but that's what I'm seeing over the last couple days.
Is it possible there's been some sort of "enhancement" in the core that might cause this? How can I check? Where should I look? Not being able to schedule is major bad news.