RAG with OpenWebUI it`s driving me mad

So, I am testing openwebui with RAG. I designed some test and after some struggle I suceed preprocesing the files and partitioning the consulting, but now, with a second test I am doing, it´s driving me mad.

I preprocess some example curriculum, some of then very short (less than 1kb) other longer (12+ kb). I have one file per curriulum and every curriculum is divided in the same 5 sections and have the same structure. The longer one was givin me problems so y focus only on it and then the things turn to worse.

For some reason, sometimes RAG only gets one fragment of the file, usually the first one. I made reranking with top K 100, minimum score 0.1 and fragments of 1500 with 300 superposition. The most annoying thing is that even with the simple prompt "list all documents in the knowledge base, showing identifier and name of file" its only shows 2 documents of 7 or even one time it get me the wrong information about the question of one file, i asked for print one section and print me other one (the first) with worng data in the middle of the section, otherwise correct. In this example for the line "titulation", it used a completely invented one, meanwhile the other lines were like the frament recovered said.

What i´m doing wrong?, as I said, with the first set of documents (technical data about dell servers) at last I had got the correct answers.