This would also have been fixed by the upgrade to 2.1.0 which is present in 5.9 Moving to POST
Verified in 5.9.2.0 Altered random_page_cost from the default of 4 to 1.1 configured replication and confirmed its working correctly.
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHSA-2018:1328