Balance 380 locking up

I have a Balance 380 HW5 that has behaved impeecably for the last 5 years. However recently, it has been locking up. The speedfusion sessions are no longer working and I cannot access the router via the web interface or SSH. The only way to recover is to remove the power and hard reboot the device.

The firmware running is the latest available 6.3.4 build 3613

Any ideas?