It sounds like a non-supported configuration.
Something to clarifiy how vPC works. I am assuming VLAN 2 is your management VLAN and VLAN900 is your vPC peer-keepalive. If you are allowing VLAN900 over the vPC peer-link, this is non-supported and the reason is, vPC peer-keepalive needs to be up before vPC peer-link to be brought up.
One solution is to use dedicated interface for vPC peer-keepalive and allow VLAN900 over it. This also required you to block VLAN900 over the peer-link.
HTH,
jerry