I think I have discovered a bug in the addon. Here's the scenario:

I open the forum checker. I close the checker without checking out. I mean I do not click on the messages and hit the "Check-Out Selected" button. Now, if there's a new reply in the topic, which I hadn't checked out, the old reply is not shown if I open the checker again. The "New Replies" field however shows the correct number of messages I haven't checked out (old messages + new messages).

Sorry I can't understand in full what do you mean.

Specially this:

Now, if there's a new reply in the topic, which I hadn't checked out, the old reply is not shown if I open the checker again.

What kind of reply do you mean? Does it mean "PREVIEW" of the message listed under topic's title?

Checker caches all previews you see on its page. If amount of previewed messages exceeds the limit set in $previewPostsMax, they won't be displayed.

What kind of reply do you mean? Does it mean "PREVIEW" of the message listed under topic's title?

Yes. Preview of message under a topic.

Checker caches all previews you see on its page. If amount of previewed messages exceeds the limit set in $previewPostsMax, they won't be displayed.

I have $previewPostsMax=100 and $limitTopics=100. There were only 7-8 topics and one message (preview) under each topic. I simply made an extra test post under one of the topics. When I re-opened the checker, only one message preview was available (the test one). The old preview of message under the respective topic was not there. But the "New Replies" field of the corresponding topic was showing as "2".

Hmm yes there was such kind of bug... I've updated the Checker's version to 2.0.6. Please download, update and report me how it works.

Thank you.

It's working fine now!

Thanks!