Urgent :: Postgresql streaming replication issue - sync mode

Hello,

We are seeing a strange issue with postgresql streaming application in sync
mode.

We are using postgresql 9.6. Old version because of some specific
requirements. We have setup cluster with master-standby using pacemaker.

When we kill master using killall -9 postgres. The failed primary has few
records extra than standby node. We have done setup with synchronous_commit
= remote_apply and have set synchronous_standby_names=server_name.

As the failed primary is having more data, How is it possible that primary
is committing transaction before they were applied on standby with
synchronous_commit=remote_apply?

Please share if you have any thoughts. Are we missing any config ?

Thanks !