Dynamic content disappears when editing email...

I'm sure there's a very simple answer to this. I have created a series of emails and have used dynamic content for relevant segments. All emails were approved and I previewed each segment to check all the dynamic content was applied.

I have gone to make some small changes to the copy and I've noticed when editing the non-default segment the dynamic content no longer appears. I've previewed the draft and this still shows as it should. Any idea why this is happening / if the dynamic content is actually there and for one reason or another not being displayed or do I have to re-do it all when editing the email?

I've attached a couple of screen grabs to show the 'preview' in comparison to what is shown when editing the email using dynamic content (different headers, etc).

@Shannon Kelly​ has recently submitted an idea to improve dynamic content functionality which if implemented would massively assist me (& I'm sure others) with day-to-day emails/editing.

Thanks,
Ellie