False triggering of PIRs overnight is completely normal due to the cooling of air, furniture, etc causing heat movements that can appear to the thermal sensor as movement.
As batteries discharge they can also become more sensitive to temperature which is why 03:30 is the classic time for PIR (and smoke detector) issues.
Alarm system PIRs include logic to only trigger after several detections (double knock), but HA PIRs are designed to trigger straight away.
You could add a conditional to the automation, or try replacing the battery. As it is an IKEA sensor, I’d also suggest enabling automatic firmware updates in ZHA in the Z-Wave integration.
If this helps, 
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