Can't identify device per port

[KEhland]

I have some switches that show the mac address of the connected device as blank if I run "show mac-address (port number)" .  I'm not sure why this happens since the command works fine for other ports on the same switch. I've seen this happen with some of the older Procurve models such as the 5406zl and 3500yl. I've tried to clear the arp table with no luck. 

Any suggestions?

[akg7]

Hi,

Could you please share device model, product number and current running software?

Thanks!