network portgroup problem

Hi I have recently created small virtual network, with 4 VM, several vSwitches and portgroups on ESXi 6.0, for a few days everything works just fine, suddenly I've got this message: This VM is attached to a network portgroup port_group2 that doesn't exist. Edit this VM and attach it to a different network.

in networking I can see this port group, when I run  esxcfg-vswitch --check-pg=port_group2

I get 1.

I haven't change any settings.

Does anybody encounter similar problem?

Does anybody have any idea where can be problem?

Thanks in advance for any tips.