vSphere Standard Switch not visible in vSphere Client

Hi,

I'm having a strange issue.

In vCenter 6 I can correctly see vSphere Standard Switches of hosts running ESXi 6.0 but I cannot see  vSphere Standard Switch 1 (only vSwitch0 and vSwitch1 is present) in all of the ESXi 5.5 hosts registered with vCenter 6.

Also vSwitch0 of some ESXi 5.5 hosts seems to lack some vmnics.

This is a "graphical" glitch since everything is working as expected.

Also checked KB 2014855 but it didn't helped.

esxcfg-vswitch -l

Returns only vSwitch0 in affected ESXi hosts.

Anyone has some suggestions?

Thank you very much in advance,

Best Regards,
Paolo