@adamlee: To troubleshoot the issue please try restarting your device, then head to Settings > Battery and Device Care > Optimise Now, followed by Memory > Clean Now. If the issue persists, are you using a particular app or apps when the problem occurs?
To help us identify any underlying software issues, I recommend sending an Error Report. To do this, please head to the Members app > Get Help > Error Report > Tap 'OK' to send System Log Data > Select the symptom, and include as much detail as possible. To ensure your logs accurately reflect the issue you're experiencing, we'd like you to submit your report within 5 minutes of encountering the problem. Our engineers will then investigate this and respond to you with a solution via the Members app.
In another thread Samsung acknowledged issues with recents and said it was with the developers and would be fixed in a future update.