With periodic reboots, suspect power first, then thermal management and firmware.

1. Is the supply big enough? Devices with IR illumination draw noticeably more at night, so working by day and rebooting by night is the classic symptom. Leave at least 30% headroom over the adapter's rated current.
2. Voltage drop: long or thin 12V runs leave too little voltage at the far end. Shorten the run, move to 24V, or take power locally.
3. PoE budget: check the switch's total and per-port PoE budget. Exceeding it causes cyclic power loss; upgrade the switch or move to PoE+.
4. Heat and ambient temperature: excessive internal temperature triggers protective restarts. Check enclosure ventilation, fans and dust filters.
5. Firmware and hardware: after ruling out the above, try a factory reset or a firmware update. If it still reboots, the PSU module or mainboard is suspect and needs repair.

Measure the voltage at the instant of reboot during diagnosis — it distinguishes a supply problem from a device problem very quickly.