This is not a common problem. Typically only some records are missing due to the wrong .QDF file was opened or there are missing other files. You need to provide more details.
Is it:# transaction entries or share price entries ?
# is it over a specific date range or all before a date or all since a date ?
Common problems are:
# you have not included all qdata.* files in the directory where you opened your qdata.QDF file. There are typically 7 QDATA.xxx files required.
# you may be missing all share price records, as the QDATA.QPH file has not been included.
# you have not opened the latest Qdata.QDF file and all transactions since that date are not in the old file.
# you were using a very old version of RPP and the file needs to be converted to the latest format. This can be an involved process.