I just figured out the reason using another means, thought that I would share the answer in case there are other people with the same problem.
It turned out that the twit-search api does not return tweets older than about a week, and also, depending on the load on the server, from time to time it can be only 24 hours! Therefore, any third-party libraries (such as twitter4j) that have a wrapper for the twitter search api will behave in a similar way.
The best way to do this is to use third-party search and indexing sites like snapbird, topsy, etc.
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