MySQL 5.6 randomly loses track of stored functions (no replies)

We have an active development commercial application that has been running in production for many years. We are heavy users of stored procedures and stored functions. The client part of the app is written in .NET and accessed through the .NET connector.
MySQL is installed on an AWS EC2 VM running ubuntu 14.04 LTS

Ever since we upgraded to MySQL 5.6 (we are running 5.6.28) from 5.5 we started randomly getting errors about MySQL unable to find a function. These are transient errors, they come in bunches and then go away. The functions are compiled in the database and run just fine right before and right after we get the transient error both through the app and from workbench.
The errors are like this:

FUNCTION l2.fn_getCustomerSetting does not exist

A separate environment running the same app, different AWS availability zone that has not been upgraded to 5.6 does not have the issue. We never had the issue prior to the upgrade. There is no DDL work being done when this happens. i.e. we are not creating nor dropping functions. There does not seem to be a pattern for the occurrence, the system is not terribly loaded.

Any ideas???

thanks.