Source SSTables may not be complete.
The source SSTables used by sstableloader (Cassandra bulk loader) may not have included all the table data.
The sstableloader streams data from SSTables on disk to a Cassandra cluster.
Before importing existing SSTables, run nodetool flush on each source node to assure that any data in memtables is written to the SSTables on disk.
For more information and instructions on sstableloader, see sstableloader.