Hi,
I actually noticed this on my iPhone 6S when updated it to iOS 12 on Monday, but I got the iPhone XS Max yesterday and I have the same exact issue. I don’t think restarting my phone, backing it up, or putting the phone in recovery mode is going to fix it. I believe this may be something Apple removed in iOS 12 and I wanted confirmation that I am not the only one with this issue or if someone knows how to bring the feature back, to let me know. Maybe I should try to re-explain what the issue is:
1. I am looking at “Safari” when a text message comes through and I get the banner at the top
2. I swipe down on the banner to read the message and reply while “Safari” is open in the background
3. But then I decide I want to answer the message through the actual Messages app, because I want to attach a photo for example
4. Before iOS 12: I could touch the open message box (from when I swiped down on the banner) and the Messages app would open right to the conversation with that individual
With iOS 12: Touching the open message box doesn’t do anything. I would have to close out of the open banner, close out of the “Safari” app, scroll to the Messages app, open the Messages app, find the conversation with the individual who texted me, and then reply.