Missing posts when new posts are added

A couple of weeks ago i wrote a calendar widget/plugin for a client, using a combination of custom post type (“event”) and posts with category “event”, then displaying the posts in the calendar with the date given in each post. I used 2 custom queries to get the relevant posts (one for category, one for the custom type). After a lot of posts where added to the calendar, we saw that some events where missing when new posts where added. Some of these missed posts returns after a few hours, some never returns. Has anyone experienced this before?

And also, is there a way I can manually send a custom query to the web page and read through the returned json-text and see if the problem is in the query/backend or in the calendar generator?