Firstly i've tried two fields in order to import the text. "introtext" and "fulltext" . In both the issues are present. Initially, I managed to import the articles sometimes almost successfully. The only issue was that "read more" appearing at the beginning of every article. Now, as you can see in the screenshots provided, the readmore cuts the text randomly, and puts itself there. Then another strange behaviour is that it duplicates the first part of the phrase and puts it bellow the "read more".
The text is HTML formatted, but this doesn't seem to be related. Also, before each import i delete previous records, and i've tried clearing cache.