Character set warning in PXC logs
It looks as though this is related to a MySQL bug, here is one discussion https://www.percona.com/forums/questions-discussions/mysql-and-percona-server/13590-character-set-warning 

Here is the bug report: https://bugs.mysql.com/bug.php?id=72543

A poster on StackOverflow reported that after updating the connector the issue was resolved, might this apply here? https://stackoverflow.com/questions/...ws-server-2012

If you are using HA Proxy, this may also be relevant, and there is a workaround at the end: https://jira.percona.com/browse/PS-1518