I have a 300 server cluster I tested on and came across these issues:

https://bugzilla.redhat.com/show_bug.cgi?id=1120442
https://bugzilla.redhat.com/show_bug.cgi?id=1120441
^ Cassandra related, aggregation

https://bugzilla.redhat.com/show_bug.cgi?id=1120445
^ Quartz, lingering alerts?

https://bugzilla.redhat.com/show_bug.cgi?id=1120422
^ Agent related, deadlock

https://bugzilla.redhat.com/show_bug.cgi?id=1120417
^ Upgrade performance related (not a new issue, just something I ran into)

This was 4.9 to 4.12.

It's not clear how critical they are but something I thought to share.