we say that from the information you gave us it is very difficult to understand if it is your mistake, if it is a problem of the original file or the one you processed.
Meanwhile I can advise you to make a purge and maybe an overkill of the base file (block or xref it is). then it would be to understand the file from where it comes from: from an export of other programs? or a normal other autocad? because often exports from other sources create blocks, retinals and (it has happened to me) also texts that weigh the disego even if apparently they are simple elements.