Users say that openfire is losing messages

My app users said that the message server is losing messages everyday.

Users chat a lot a day, and can lose about 2-3 messages a day per each.

I want to know if anyone has the same problem like this.

My server is centos 6.5

openfire 3.10.3

DB mysql

Daily users is just about 1-3k, not all chat at the same time