I would suggest you to have a look at this link

For the release of the CU5 for SQL Server 2012 SP2 , the release date ( according the same post ) is end of March 2015.

An advice from the SQL Server Support Center : to avoid to install isolated CU and to prefer to wait for the release of the next SP ( as the Support is doing full tests for a new Service pack , it is not the same thing for a CU for which the tests are done less heavily , except to search incompatibilities between the KBs included in the CU ). It is why sometimes , some KB included in the last CUs are not included in a new SP.

At the end of the article , you should find

( about the problem of the databases participating to AlwaysOn Availability Groups (aka AG), the AG might be reported as NOT SYNCHRONIZING )

Don't forget to read the comments at the end of the article.

I hope that I have been understandable despite my poor English language.