Postgresql 9.6.12 switchover failing

Hi everyone,

I have a strange issue on my testing postgresql cluster.
I have 2 nodes with postgresql 9.6.12 on RHEL7 .
The slave is being updated through hotstandby streaming replication.

In the past ( 9.6.8 and earlier), I was able to do a clean switchover
without any issues.
I did the following steps:
1. Check if the standby is uptodate
2. If so, shutdown the primary
3. pg_ctl promote the standby
4. Create a recovery.conf on the former primary and start the instance.

This worked just fine, with in the end the roles of the nodes changed.

Now I have version 9.6.12 and am trying to do the same.
The steps 1 to 3 works just fine.
But bringing up the old primary as a slave doesn't work. I get errors (
like >FATAL: requested timeline 5 is not a child of this server's history)
and the instances shuts down automatically.
I know I can fix it with pg_rewind ( have done it), but am confused about
this.

Does anyone have the same issue? Or has anyone encountered the same problem?

Thanks in advance.
regards,
Marian