I had the same problem today where only the first row from my data was being printed on the report but the raw xml file in the right panel in Preview mode showed all rows were being returned. I followed @PGriffith 's suggestion from Report not displaying row-0 - #5 by MC2338 and re-created the table. That fixed the problem for me. I did not re-create the table to be identical to the first one though.
Looking at the original post, it looks like similar to me he has two or more groups of data (Row and query) for just one query. I imagine somewhere in the design process manipulating grouped data causes a bug, and re-creating the table without all the trial-and-error steps that went into creating it foregoes triggering that bug.