Not able to display messages on UI using JPublish and java

We are using jpublish and velocity template for UI and java for backend.
Currently i am facing problem that i am not able to display error message on UI. I used list for adding error in java and display on UI if any validation fail. But we have error in list but not displaying UI.
For displaying logic i iterating list on UI.
Before its use to display on UI but now its not showing and there is no change in code.
Is there any configuration problem.

Due to some reason i can not provide the code.