Cannot assign virtual address to a traffic group

This was the plan:

BIGIP1-A TG1 BIGIP2-A TG2 BIGIP3-S TG3

And all the TGs should failover to each other when the devices go down.

However, on the BIGIP3 I cannot assign the VA to the TG3 and hence when TG3 fails over the Virtual server with it doesn't failover.

But the TG3 has a floating self IP which I assigned to it, but on assigning the VA and updating it just reverts back to traffic-group-local.

In TG3 cli all I see is the FIP

root@(bigip3)(cfg-sync In Sync)(Active)(/Common)(tmos) show cm traffic-group TG3 failover-objects
----------------------------------------------------
CM::Traffic Group
----------------------------------------------------
Object Type  Object Path               Traffic Group
----------------------------------------------------
self IP      /Common/TG3-internal-FIP  TG3

    root@(bigip3)(cfg-sync In Sync)(Active)(/Common)(tmos) show cm traffic-group TG3 all-properties

--------------------------------------------------------------------------------------------
CM::Traffic-Group
Name  Device          Status   Next    Load  Next Active  Times Became  Last Became
                               Active        Load         Active        Active
--------------------------------------------------------------------------------------------
TG3   bigip1.akm.com  standby  true    -     1            2             2018-Jul-21 14:16:55
TG3   bigip2.akm.com  standby  false   -     -            0             -
TG3   bigip3.akm.com  active   false   1     -            2             2018-Jul-21 14:21:06

Any ideas to sort this please??