Symptom:
HSRP VMAC is not programmed with the G flag in the software MAC table on vPC peer who is HSRP standby:

RTP-Agg2# sh hsrp brief
*:IPv6 group   #:group belongs to a bundle
                     P indicates configured to preempt.
                     |
 Interface   Grp  Prio P State    Active addr      Standby addr     Group addr
  Vlan2       2    0      Standby  2.2.2.2          local            2.2.2.3         (conf)


RTP-Agg2# sh mac ad ad 0000.0c07.ac02
Legend:
        * - primary entry, G - Gateway MAC, (R) - Routed MAC, O - Overlay MAC
        age - seconds since last seen,+ - primary entry using vPC Peer-Link,
        (T) - True, (F) - False
   VLAN     MAC Address      Type      age     Secure NTFY Ports/SWID.SSID.LID
---------+-----------------+--------+---------+------+----+------------------
* 2        0000.0c07.ac02    static       -       F    F  vPC Peer-Link

Conditions:
This is condition is seen when the HSRP configuration includes a track object and the decrement value will set the priority to less than or equal to zero when the track object is in a down state:

interface Vlan2
  hsrp 2
    priority 80
    ip 2.2.2.3
    track 10 decrement 80 <<<<<<< This decrement value is greater than or equal to the configured or default priority