Hi,
events have a certain minimum height if "Settings > Display and Use > Day view > Enforce a minimum height for entries, e.g. to ensure that events without a duration are displayed at all." is turned on. This makes your 30 minute event higher than it usually would be. This way it overlaps with the next upcoming event, which causes both events to be displayed side-by-side instead of one after another.
So you can either turn that option off or you can make the height of each hour higher, either under "Settings > Display and Use > Day view > Height of an hour" or by using the pinch gesture. Then also the short 30 minute event should be displayed over the full width.
Please don't hesitate to contact me again if you have further questions!
Kind regards
Dominique Gunia