Unfortunately, there is no way to check the logs after the restart of the router. One thing that you could do is export the log content into some kind of server, but that would be a lot of hassle for such an issue.
I will need you to do some things before we act:
1. Could you make sure that you're running the latest firmware version of the device?
2. Make sure that the power supply that you're using with the device is not faulty (If you have any other power supply - please try using it instead).
3. Make sure that the groundings of the device are fine (grounding wire inside power supply cable).
4. Also, make sure that you're using your device fully cased and not naked. Make sure everything is tight (antennas and screws of the case) and that the router doesn't get any hard power surges into it when power failure happens.