Fwd: upgrade to PG11 on secondary fails (no initdb was launched)

Hey,
I have 2 nodes that are configured with streaming replication (PG 9.6,
repmgr 4.3).
I was trying to upgrade the nodes to PG11 with the doc -
https://www.postgresql.org/docs/11/pgupgrade.html
Everything goes well until I try to start the secondary and then it fails
on the next error :

2019-05-23 04:17:02 EDT 23593 FATAL: database files are incompatible
with server
2019-05-23 04:17:02 EDT 23593 DETAIL: The database cluster was
initialized with PG_CONTROL_VERSION 960, but the server was compiled with
PG_CONTROL_VERSION 1100.
2019-05-23 04:17:02 EDT 23593 HINT: It looks like you need to initdb.
2019-05-23 04:17:02 EDT 23593 LOG: database system is shut down

I upgraded the primary, then I run the rsync command in the primary :
rsync --archive --delete --hard-links --size-only --no-inc-recursive
/var/lib/pgsql/data /var/lib/pgsql/11/data/
secondary_ip:/var/lib/pgsql/data/

in the secondary I checked the version file and it was 11 :
[secondary]# cat PG_VERSION
11

Any idea how to handle it ? I'm sending it to the performance mail list
because no one answered it in the admin list ..