If you are planing to go live with a client soon, on that particular version, it is mandatory for HA to install BP4 (220.127.116.11.4) - 13647251 and the following patches.
*do a quick check of each patch here to ensure you are using these components.
Note that you need to download them for the 18.104.22.168.4 version of WebCenter and install them after the BP. You'll need to update OPatch(6880880) as well.Make sure you download the version for your environment.
The patches fix critical issues in Java Object Cache, serialization and deadlock issues which occur under medium load. I recommend you apply these patches as soon as possible after install.
If you are on 22.214.171.124.0, you have the equivalent of BP4 already with a couple extra features. You may still need the individual patches mentioned.
I will make a broader post about HA soon.