iPhone X, iOS 11.4, mobile safari, chrome and Discourse app:
I see lines between topics just fine in your screenshot? You mean that one in the middle?
I am seeing the last visit just fine on meta with iPhone so either this is a theme issue or, I dunno.
Maybe specific to the “solved” plugin topics since that is where it was in your screenshot.
I was wondering if maybe the unread marker was adding just enough height to overflow beneath / above the line, but I couldn’t think of why the “last visit” line might become hidden at the same time.
If it is a combination of an unread marker on the topic just above the last visit line, it won’t be easy to repro.
We can not reproduce this.