If you are finding that one event is split up into multiple files, then the solution is to increase the post-capture time under Preferences - Cameras - Motion Capture.
Or, if you want all motion events throughout the day recorded to the same file, you can set the "Capture type" to "One movie per day" (also under Preferences - Cameras - Motion Capture).
If the issue is that one event is split into multiple files, then increasing the post-capture time (e.g. to 30 or 40 seconds) should significantly reduce the occurrence of this.
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Or, if you want all motion events throughout the day recorded to the same file, you can set the "Capture type" to "One movie per day" (also under Preferences - Cameras - Motion Capture).