SQLite Forum

DB with Fts4 passes integrity check, but throws SQLITE_CORRUPT_VTAB (database disk malformed) whenever column is queried
Corrupt or missing records in the shadow tables used by fts4.

You might be able to fix things by rebuilding the index:

        INSERT INTO fts3_tbl_name(fts3_tbl_name) VALUES('rebuild');

If you're doing new development, fts5 is much better than fts4.