I think the problem is that.
To synchronize access policies between multiple devices, you configure a Sync-Only device group, which includes the devices between which you want to synchronize access policies. Device group setup requires establishing trust relationships between devices and creating a device group. You set the devices in each group to use Automatic Sync and Full Sync, and then synchronize access policies one at a time, resolving conflicts as you go.
Important: Sync-Only groups must be configured before you pair Active-Standby devices. To add an Active-Standby device pair to a Sync-Only device group, first you must reset the trust between the devices. Next, you must remove the devices from the Sync-Failover device group. Next, you must add both devices to a Sync-Only device group. Finally, add the devices as an Active-Standby pair to the Sync-Failover group.
https://techdocs.f5.com/kb/en-us/products/big-ip_apm/manuals/product/apm-implementations-11-5-0/4.html#conceptid