My site has 10-15 users logged in but my freichat only shows 4 online. What can be done to change this?

FreiChatX shows users in realtime while your site shows also the users that have already left your site a while ago.

At times there are users chatting in my shout box but aren't show as being online in freichat? How can this be corrected?

do you have the chat restricted to buddies.
this might not show all the online users.

I have it set to users, not just buddies. Any other suggestions?

I really can't say much without seeing it myself.
But why don't you try logging in with 3-4 different browsers, also try logging in from different computers and see if you can reproduce the bug.
If you can reproduce the bug,
Please provide us with dummy accounts via the contact us form, we will see what is happening exactly.