mySQL data table seems to stuck at 16777215 rows
The maximum value for your auto_increment 'seq_number' field is 16777215.  You should make this field use an int or a bigint if you need more that 16,777,215 records.

See the MySQL Documentation for info about the mediumint(9) format.

https://dev.mysql.com/doc/refman/5.0/en/integer-types.html