I found the reason of losing all virtual parts in my assemblies. It is Pack&Go command. After it, all virtual parts are lost in both assemblies, they become greyed out in feature tree after reopening of assembly. When I try to open virtual part I get the following message.
Hi all,
If you are encountering this problem it's important you report it to your reseller for investigation. It sounds that the following SPR likely covers the problem, but your reseller can verify this by working with our Tech Support team.
SPR 1018568: Systems - Pack and Go: Some virtual components in Pack and Go are losing file references (suppressed).