One other thought -- I already tried to reproduce with S Planner on a Note 3 + 5.0, but couldn't...
Still, maybe you could let me know the details of your event, so I could try an event exactly like that:
- Repeating or not, and if repeating, what exact repeat pattern
- Custom event color, yes or no
- Any attendees or not
- Reminders, yes or no, exact value ("at time of event", or "XXX in advance").
- Last but not least, the device's Android version, 4.4, 5.0...?