Could expand on "device crash"? Does it loose internet connectivity or becomes completely unresponsive?
What configuration changes have you made within the device?
Do you have any additional packages installed?
What is the environment in terms of temperature and humidity, where the devices are being stationed?
What firmware version are the devices running?
Could you send me a troubleshoot file from one on the problematic devices? To generate the file, access router's WebUI, go to System -> Administration -> Troubleshoot section and download troubleshoot file from there.