The default IP of the switch is 192.168.0.1. Check if there is any IP conflict in your network. And when you failed to access the switch, can you still access internet? Is there any change in your network environment?

@Somnus 

The switch has it's own IP to suit the network.  There is no conflict.

All devices using the switch do not lose LAN connectivity.  Data throughput is fine.  Only management access via browser or config utility is affected.

Interestingly pressing the reset switch has no effect, no matter how long it's held in.  No LED's flash to indicate reset.

A power-cycle brings everything back to normal.

Seems the inner software is down periodically. How often does the issue happen? Is there any advanced configuration on the switch?

Seems the inner software is down periodically. How often does the issue happen? Is there any advanced configuration on the switch?

 

Somnus wrote

Seems the inner software is down periodically. How often does the issue happen? Is there any advanced configuration on the switch?

Exactly.  But what is the cause?

 

Not sure how often issue appears.  Only had the switch 5 months.  So far, only twice as I rarely need to access management.  Just a hassle that when I need access, it's not always available.

Nothing advanced.  Only PoE on 4 ports.